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1988 Stratigraphic Framework and Sedimentary Facies of a Clastic Shelf-Margin: Wilcox Group (-), Central . Philip Lowry Louisiana State University and Agricultural & Mechanical College

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Recommended Citation Lowry, Philip, "Stratigraphic Framework and Sedimentary Facies of a Clastic Shelf-Margin: Wilcox Group (Paleocene-Eocene), Central Louisiana." (1988). LSU Historical Dissertations and Theses. 4516. https://digitalcommons.lsu.edu/gradschool_disstheses/4516

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Stratigraphie framework and sedimentary facies of a clastic shelf-margin: Wilcox Group (Paleocene-Eocene), central Louisiana

Lowry, Philip, Ph.D.

The Louisiana State University and Agricultural and Mechanical Col., 1988

UMI 300 N. Zeeb Rd. Ann Arbor, M I 48106

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. STRATIGRAPHIC FRAMEWORK AND SEDIMENTARY FACIES OF A CLASTIC SHELF-MARGIN: WILCOX GROUP (PALEOCENE-EOCENE), CENTRAL LOUISIANA

A Dissertation

Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy

in The Department of Geology

by

Philip Lowry B.Sc. University of Ulster, 1978 M.Phil. University of Ulster, 1982 May, 1988

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS

I would like to thank Dr. Thomas F. Moslow who acted as chairman of my dissertation committee for providing me with the opportunity to work on this project. I am also endebted to Dr. Clyde Mocre, Dr. Dag Nummedal, Dr. David Prior, Dr. Jeffrey Nunn, and Dr. Julius Langlanais for the input they provided as members of my committee. In particular, 1 would like to express my gratitude to Dr. Dag Nummedal who gave me the opportunity to pursue my doctoral work at LSD and helped broaden my knowledge of the many facets of modern and ancient depositional systems. I would also like to extend my sincere thanks to Dr. Indra Bir Singh for his advice and insight during many long hours of discussions.

Rowdy Lemoine, Sam Reed, Anne Brunett, Brian Ripple, Danny Peace, Mary Lee Egged, and Clifford Duplechen assisted me in various aspects of this project. My fellow graduate students Bruce Kofron, Michael DiMarco, Steven Jones, Ezat Heydari, Kathleen Farrell, Dave Evans, and Steve Johansen provided many helpful suggestions over the years and their input is greatly appreciated.

I would like to thank the following companies and institutions for their financial support: Atlantic Richfield Company, Mobil Oil Corporation, Shell Companies Foundation, LSU Department of Geology and LSU Basin Research Institute. Amoco Production Company and Sun Exploration and Production Company provided me with access to cores and data pertinent to my study area which is most appreciated. 1 would also like to thank Mike Center of Paleo Data in for providing me with paleontological data free of charge. I would like to thank my family for their support throughout my graduate studies. The support of my parents and my wife’s parents and Uncle Paul

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. McDonald can never be repaid, hinally, and most importantly of all, I would like to thank my wife, Dianne, for her constant love, support, and encouragement.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DEDICATION

This dissertation is dedicaited to my wife Dianne, truly a unique lady.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS

Acknowledgements ...... ii Dedication ...... iv Table of Contents...... v List of Tables...... x List of Figures...... xi Abstract...... xxiii Introduction ...... 1 Stratigraphie and structural framework of an ancient clastic shelf-margin: The Wilcox Group (Paleocene-Eocene), central Louisiana...... 5 Introduction ...... 7 Geologic background ...... 8 Pre-Wilcox stratigraphy ...... 8 Wilcox stratigraphy ...... 11 Lower Wilcox Middle Wilcox Upper Wilcox Depositional sequences and sequence stratigraphy ...... 16 Recognition criteria for depositional sequence boundaries ...... 20 Introduction ...... 20 Recognition criteria ...... 22

Lateral continuity and facies relationships Marine fauna Nature of the lower contact Wilcox depositional sequences...... 25 Wilcox shelf-margin stability ...... 28

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Wilcox submarine canyon system...... 35 General morphology and stratigraphie relationships ...... 35 Model of canyon development ...... 45 Discussion...... 47 Conclusions...... 53 References...... 56 Sedimentary facies of the uppermost Wilcox shelf-margin trend;

south-central Louisiana...... 65 Introduction ...... 67 Wilcox in Louisiana...... 67 Stratigraphie nomenclature ...... 70 Regional geologic setting ...... 71 Fordoche field ...... 73 Development history ...... 73 Reservoir geometry and growth-faulting ...... 75 Cored sedimentary facies ...... 78 Vertical sequence...... 78 Facies F Facies E Facies D Facies C Facies B Facies A Depositional processes and events ...... 100 Depositional model ...... 103 Reservoir quality...... 105 Conclusions...... 10P

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. References...... 11 o

Sedimentary facies from a shoreface sequence in a stable shelf- margin setting: The Wilcox Group (Paleocene - Eocene), central Louisiana.,...... 115 Introduction ...... 117 Wilcox depositional sequences ...... 119 Genera! background ...... 119 Stratigraphie relationships of the 1st Wilcox' depositional event ...... 120 Geometry of the '1 st Wilcox' ...... 123 Facies of the '1st Wilcox' sandstone ...... 128 Facies A...... 128 Facies B...... 130 Facies C ...... 137 Facies D ...... 137 Facies E...... 142 Previous interpretation ...... 142 Shelf versus iagoonal mudstones ...... 147 Introduction ...... 147 Micropaleontological evidence ...... 148 Biogenic activity ...... 148 Vertical sequence...... 149 Character of the channel facies ...... 152 Proposed depositional model ...... 159 Introduction ...... 159 Vertical sequence...... 159

Modern analogue ...... 161

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Channel facies ...... 164 Comparison with a growth-faulted margin ...... 167 Shelf shoal versus truncated shoreface ...... 170 Conclusions...... 174 References...... 175

Numerical simulation of stratigraphie sequences and shoreface sequences from a clastic shelf-margin ...... 183 Introduction ...... 185 Simulation model for stratigraphie sequences ...... 188 Introduction...... 188 Wilcox depositional sequences ...... 191 STRATSIM: program structure ...... 193 Modeling the Tertiary sequence using high- order global sea-level cycles ...... 196 Simulation of Wilcox depositional sequences ...... 205 Introduction ...... Sequences resulting from third-order and glacial-type global sea-level cycles ...... a) constant sea-level amplitude and variable wavelength b) constant wavelength and variable amplitude Sequences resulting from variations in the rate of eustatic sea-level fall a) Stair-step sea-level fall -106 year intervals b) Stair-step sea-level fall - 500,000 year intervals Discussion...... 216 Biased random-walk shoreface simulation model ...... 221 Introduction...... 221

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Program structure...... 225 Program results ...... 231 Introduction Temporal variation in the sandbody geometry Shoreface response to variable rates of sea-level change Comparison of transition zone facies which formed under rising versus falling sea-levels Discussion

Conclusions...... 248 References...... 250 Bibliography ...... 254 Appendix A - Listings of computer programs STRATSIM and DEPSI.M ...... 273 Appendix B - Porosity, permeability, oil and water saturation data

from core plugs and sidewall samples Lockhart Crossing Field ...... 293

Appendix C Listing of wells used to construct regional

structure map and cross-sections ...... 326

Appendix D-Regional well-log cross-sections (Located in

cover pocket) ...... 333

Vita...... 334

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES

Table 1.1 Benthic foramlnifera from shale interval F ...... 24

Table 2.1 Sedimentary characteristics and relative reservoir quality of cored facies ...... 79

Table 3.1. Benthic foraminifera from facies A ...... 131

Table 3.2. Benthic foraminifera from facies C ...... 139

Table 4.1 Summary of various types of sea-level fluctuations and their durations and amplitudes. (Modified after Nummedal, 1983) ...... 194

Table 4.2 List of simulations performed by program STRATSIM ...... 199

Table 4.3 Causes, magnitude and rates of global sea-level change. (After Pitman and Golovchenko, 1983) ...... 219

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES

Figure 1.1 Generalized structure contour map of the top of the Wilcox Group In Louisiana. Note the location of two well-defined oil and gas production trends. The shallow Wilcox trend In LaSalle, Concordia and Catahoula Parishes Is primarily dip- oriented. The deep Wilcox extends through Livingston, East Baton Rouge, Pointe Coupee and Beauregard Parishes ...... 9

Figure 1.2 General location of early and Tertiary shelf- edges within the northern rim of the Gulf of basin. (After Martin, 1978) ...... 10

Figure 1.3 Schematic dip cross-section through early Cretaceous shelf- marglns from the northern rim of the Gulf of Mexico basin. This profile Is located In south ; however, the broad stratigraphie relationships are similar along the shelf-margin. (After Hendricks and Wilson, 1967) ...... 12

Figure 1.4 Dip cross-section through lower Cretaceous shelf-edge In central Louisiana showing facies relationships of the overlying Tuscaloosa formation. (After Berg, 1982) ...... 13

Figure 1.5 Schematic Wilcox subsurface divisions showing the fluvlal- domlnated lower Wilcox overlain by a major marine transgresslve sequence (the 'Big Shale'). The upper Wilcox Is believed to be composed of a series of wave-dominated deltaic complexes ...... 15

Figure 1.6 Schematic diagram of the lower Wilcox Holly Springs deltaic complex In Louisiana and . (After Galloway, 1968) ...... 17

Figure 1.7 Definitions of depositional episodes and depositional events according to Frazier. (After Frazier, 1974) ...... 19

Figure 1.8 Regional strlke-orlented well-log cross-section showing depositional sequences (W-1 through W-V11) and major transgresslve shale units (A-F) within the Wilcox of central Louisiana. The upper boundary of each sequence Is defined by a regional transgresslve disconformlty. (See #4 on Fig. 1.17 for location of cross-section)...... 21

FIc jre 1.9 Regional dip-oriented cross-section showing Wilcox depositional sequences and their relationship to the early Cretaceous reef trend and Tuscaloosa shelf-margin In central Louisiana. (See #2 on Fig. 1.17 for location of cross-section)...... 23

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 1.10 Schematic diagram showing inferred facies relationships which result from differences between subsidence and deposition. The Wilcox sequences shown in Figure 1,9 most closely approximate the condition shown in part b. (Modified after Curtis, 1970) ...... 27

Figure 1.11 Schematic diagram depicting major categories of clastic shelf-margins within the Gulf of Mexico basin. (After Winker, 1984) ...... 29

Figure 1.12 Dip-oriented sandstone percentage profile through the Wilcox in central Louisiana. (See #1 on Fig. 1.17 for location). 30

Figure 1.13 Dip-oriented sandstone percentage profile through the Wilcox in central Louisiana. (See #2 on Fig. 1.17 for location). 31

Figure 1.14 Dip-oriented sandstone percentage profile through the Wilcox in central Louisiana. (See #3 on Fig. 1.17 for location). 32

Figure 1.15 Generalized lithologie cross-section through the Tertiary of the Texas coastal plain showing large-scale growth-faulting. Compare this figure with that depicted in Figure 1.14 ...... 33

Figure 1.16 Reflection seismic profile across the Wilcox and early Cretaceous shelf-margins from western-central Louisiana. Note the relatively undisturbed character of the Wilcox reflectors and relative positions of the Tuscaloosa and pre- Tuscaloosa lower Cretaceous shelf-edge. (See #6 on Fig. 1.17 for location of line)...... 36

Figure 1.17 General map of central Louisiana showing relative positions and stability regimes of the Wilcox shelf-margin. It appears that the lower Cretaceous shelf-edge in western Louisiana is located downdip from the Edwards-Sligo Reef Trend. (Also see Berg, 1982). The central unstable region of the margin corresponds to the location where the Wilcox prograded significantly beyond the pre-existing margins. 1. Location of profile shown in Figure 1.12. 2. Location of profiles shown in Figure 1.9 and Figure 1.13. 3. Location of profile shown in Figure 1.14. 4. Location of profile shown in Figure 1.8. 5. Location of profile shown in Figure 1.20. 6. Location of profile shown in Figure 1.16 ...... 38

Figure 1.18 a) Strike-oriented well-log cross-section through localized thickening of shale inteval E. (See Fig. 1.8). b) Strike-oriented cross-section through the Yoakum channel system in the Wilcox of Texas. (After Hoyt, 1959) ...... 39

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Reproduced with permission of the copyright owner Further reproduction prohMed without permission. Figure 1.19 Strike-oriented profile through the submarine canyon system in Avoyelles Parish. (See Fig. 1.17 for location) ...... 40

Figure 1.20 Reflection seismic profile through the St. Landry Canyon. (See #5 on Fig. 1.17 for location)...... 43

Figure 1.21 Comparison of Avoyelles/St. Landry Canyon profile to Yoakum channel profile ...... 44

Figure 1.22 Comparison of St. Landry Canyon and Yoakum channel profiles with some modern canyon profiles ...... 46

Figure 1.23 Generalized sequence of events leading to the development of the stable Wilcox shelf-margin. a) Initial location of k "'er Cretaceous shelf-margin. b) Major fall in sea-levv.' and deposition of sediments beyond the shelf-edge into deep v'ater. c) Progradation of shallow marine elastics onto and beyond the shelf-edge. d) Continued rise in sea-levei leading to the deposition of pelagic and hemipelagic muds and the extensive upper Cretaceous chalk sequences. e) As sea-level began to fall again, Midway and Wilcox elastics were deposited on top of the stable carbonate platform. f) A sea-level rise at the end of Wilcox deposition led to the deposition of pelagic and hemipelagic muds of the Claiborne Group on top of the Wilcox ...... 50

Figure 1.24 Stratigraphie relationships of the Wilcox supersequence within central Louisiana. Each sequence represents approximately 106 years. For most of Wilcox deposition, progradation did not bypass the Cretaceous shelf-margin ...... 51

Figure 1.25 Reflection seismic profile across the shelf-margin. This figure depicts the probable stratigraphie relationships of the Wilcox Group to the underlying shelf-margins in the stable region of the margin ...... 54

Figure 2.1 Generalized Gulf Coast Cenozoic stratigraphie column ...... 68

Figure 2.2 Location map of oil and gas fields in central Louisiana showing structural contours on top of the Wilcox. The enclosed region in the lower part of the map is the study area for this investigation and shows the location of regional strike and dip cross sections in Figures 2.5 and 2.6 (modified from Oil and Gas Map of Louisiana, Louisiana Geological Survey, 1981) ...... 69

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.3 Map of lower Cretaceous, Tuscaloosa/Woodbine, and Wilcox shelf-margin trends in the northern Gulf Coast with locations of Yoakum Channel and St. Landry Canyon (modified from Winker, 1982) ...... 72

Figure 2.4 Wilcox "type-log" for Fordoche Field from the N. Smith Jr. #8 well. Core sequences from the W8 Sandstone (stippled) are examined in this study. Main producing intervals are labeled (Modified from Eckles et al., 1981) ...... 74

Figure 2.5 Regional strike-oriented cross-section (A-A') through the uppermost Wilxcox of the study area (see Fig. 2.2 for location of section). The W8 Sandstone is indicated by a stippled pattern. Note that the W8 overlies a thick sandstone sequence that pinches out along strike to the east and west ...... 76

Figure 2.6 Regional dip-oriented cross-section (B-B') through the uppermost Wilcox of the study area (see Fig. 2.2 for location of section). The W8 Sandstone is stippled in the Sherburne Land #1 well which was used to define the along-strike continuity of the W8 in cross section A-A' (Fig. 2.5). Note rapid lateral facies changes in the W8 in a downdip and updip direction ...... 77

Figure 2.7 Map of Fordoche Field. Note locations of cored wells including the N. Smith Jr. #8 well in T6S, R8E, sec. 41. Cross- section C-C is through the central axis of the field ...... 81

Figure 2.8 Schematic core description for N. Smith Jr. #8 well. This sequence is interpreted to be characteristic of the W8 Sandstone ...... 82

Figure 2.9 Core photograph of 13, 172-13, 181 ft (4,015-4,018 m) from the N. Smith Jr. #8 well showing the lowermost portions of facies F and uppermost portions of facies E. Lenticular bedding (a), glauconite pellets (b), and siderite concretions (c) are shown. Core is approximately 3 in. (7.5 cm ) in diameter...... 84

Figure 2.10 Core photograph of 13,181-13, 192 ft (4,018-4,021 m) from the N. Smith Jr. #8 well. Note sharp contact (arrow) between facies C and facies D. Carbonate concretions (d) are common features in facies D ...... 85

Figure 2.11 Core photograph of 13,192-13,203 ft (4,021-4,024 m) from the N. Smith Jr. #8 well showing the massive-appearing sandstones characteristic of facies C ...... 86

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.12 Core photograph of facies C from 13,203-13,213 ft (4,024- 4,027 m) in the N. Smith Jr. #8 well. Note decrease in the amount of burrowing upward...... 87

Figure 2.13 Core photograph of 13,213-13,223 1ft (4,027-4,030 m) from the N. Smith Jr. #8 well. Note location of Ophiomorpha burrow at 13,214.5 ft (see Fig. 2.19A) ...... 88

Figure 2.14 Core photograph of 13,223-13,233 ft (4,030-4,033 m) from the N. Smith Jr. #8 well showing characteristic features of facies B. Note amalgamation of sandstone beds (e) at 13,224 ft and discrete sandstone beds at 13,224.5 ft (see close-up photo in Fig. 2.20A) ...... 89

Figure 2.15 Core photograph of facies B from 13,233-13,243 ft (4,033- 4,036 m) in the N. Smith Jr. #8 well. Note Planolites burrow (f), and Teichichnus burrow (g). Thin discrete sandstone bed at 13,237.2 ft is shown in close-up photo in Figure 2.20C ...... 90

Figure 2.16 Core photograph of 13,243-13,250 ft (4,036-4,039 m) from the N. Smith Jr. #8 well. Note Terebellina burrow (h) and Chondrites burrow (I) In facies B. Load-casted ripple at 13,245.8 ft Is shown In detail In Figure 2.21 A ...... 91

Figure 2.17 Core photograph of facies A from 13,250-13,260 ft (4,039- 4,042 m) in the N. Smith Jr. #8 well. Note contorted (j) and lenticular (k) bedding. Contorted bedding at 13,251.6 ft Is shown in detail in Figure 2.21 C ...... 92

Figure 2.18 Close-up photograph of calcareous sandstone from facies D (see Fig. 2.10 at 13,182 ft). Note abundant shell fragments ...... 94

Figure 2.19 [A] Close-up photograph of burrowed sandstone from facies C (see Fig. 2.13 at 13,214.5 ft). Note abundance of Ophiomorpha burrows (1). [B] X-ray radiograph of cored Interval In Figure 2.19A. Note abundance of burrowing and lack of any preserved physical sedimentary structures ...... 96

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.20 [A] Close-up photograph of thin (<5 cm) very fine-grained sandstone bed in facies B (see Fig. 2.14 at 13,224.5 ft). [B] X- ray radiograph of cored interval in Figure 2.20A. Note faint horizontal to low-angle planar-tabular laminations at the base of the photo (m). [0] Ciose-up photograph of thin (<5 cm) very fine-grained sandstone bed from facies B (see Fig. 2.15 at 13,237.2 ft). Note sharp lower contact (n) and burrowed upper contact (o). [D] X-ray radiograph of cored interval in Figure 2.200. Note horizontal laminations and normal grading within laminations. Arrows represent coarser-grained (light) and finer-grained (dark) sediment. Also, note burrowing which has subsequently destroyed laminations.(p) ...... 97

Figure 2.21 [A] Close-up photograph of a load-casted ripple from facies A (see Fig. 2.16 at 13,245.8 ft). [B] Sketch of cored interval in Figure 2.21 A. Note truncation surfaces of individual laminations. [C] Close-up photograph of cored interval in facies A ilustrating contorted bedding resulting from soft- sediment deformation (see Fig.2.17 at 13,251.6 ft) ...... 99

Figure 2.22 Block diagram depicting a paleogeographic reconstruction of the depositional setting for the W8 Sandstone, specifically a prograding shoreface system at the shelf edge ...... 104

Figure 2.23 Reservoir characteristics and downhole electric log signatures for cored sedimentary facies from the W8 Sandstone interval in the N. Smith Jr. #8 well. Petrophysical data is from core plugs. Note extremely high permeability at the top of facies C and in the thin beds at 13,230 ft in facies B 106

Figure 3.1 General location map of Louisiana and Lockhart Crossing field within Livingston Parish ...... 118

Figure 3.2 Stratigraphie relationships of the Wilcox supersequence within central Louisiana. Each sequence represents approximately 106 years. For most of Wilcox deposition, progradation did not bypass the Cretaceous sheif-margin ...... 121

Figure 3.3 Dip cross-section through W-V11 sequence in St. Helena and Livingston Parishes. (See Fig. 3.1 for location). Depositional events are marked 1-6; the '1st Wilcox' is event #5...... 122

Figure 3.4 Net sandstone map of depositional events 1-3 within sequence W-Vl 1 in central Louisiana...... 124

Figure 3.5 Net sandstone map of depositional events 4-6 within sequence W-V11 in central Louisiana...... 125

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 3.6 Isopach map of the '1st Wilcox' sandstone in central Louisiana. (See Fig. 3.5 for location) ...... 126

Figure 3.7 Dip-oriented profiles through the '1st Wilcox' sandstone. Note the highly assymetric profile with the steepest side occurring on the basinward edge of the interval. (See Fig.3.6 for location of profile) ...... 127

Figure 3.8 Close-up view of a sandstone interbed within facies A. Note the horizontal laminations throughout the bed and the occurrence of Planolites burrows near the upper contact ...... 129

Figure 3.9 Frequency of beds greater than 1 cm thick in facies A with depth. a) A. Thom #1 b) State Lease 7729 #1 c) Crown Zellerbach #1 ...... 132

Figure 3.10 Schematic core description of the A. Thom #1 core. Note the missing core intervals. Also note how facies E unconformably overlies facies B...... 134

Figure 3.11 a) X-ray radiograph of a medium sand-sized bed which occurs within facies B. b) Close-up photograph of small mudstone clasts which occur near the upper contact of facies B ...... 135

Figure 3.12 a) X-ray radiograph of rare horizontal laminations which occur within facies B. b) Close-up photograph of extremely rare trough cross- stratification from facies B ...... 136

Figure 3.13 a) Close-up photograph of horizontally laminated mudstone of facies C. b) Close-up photograph of facies C, this time showing how extensively burrowed the facies may appear ...... 138

Figure 3.14 Close-up photograph of the O. M. Barnett core. Note facies B and D and the appearance of relatively large angular mudstone clasts. Note the range in size of mud clasts and the preservation of internal bedding within the clasts ...... 141

Figure 3.15 Close-up photographs of bedding types from Facies E ...... 144

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 3.16 X-ray radiograph of burrows from facies E near the contact with facies B. a) Oblique sand-filled burrows with mud-lined walls. b) Vertical sand-filled burrows. The white specks depict glauconite pellets within the burrow-fill. Note how the surrounding laminae have been bent downward by the burrowing organism ...... 146

Figure 3.17 Depositional models for the transgressed shoreface sequence. a) Erosion of shoreface by tidal inlets and back-barrier channels. (After Reinson, 1984). b) Erosional shoreface retreat model. (After Swift, 1968) ...... 151

Figure 3.18 Dip-oriented well-log cross-section through the probable axis of the channel system which transects Lockhart Crossing field. (See Fig. 3.1 for location) ...... 154

Figure 3.13 Strike-oriented well-log cross-section through the probable axis of the channel system which transects Lockhart Crossing field. (See Fig. 3.1 for location) ...... 157

Figure 3.20. Facies relationships within the channel which transects the Lockhart Crossing field ...... 158

Figure 3.21 Probable modern analogues for the '1st Wilcox' interval at Lockhart Crossing. a) Coast of Nayarit, fyiexico: a regressive strandplain complex (After Curray et al, 1969). b) Tabasco beach ridge complexes, Mexico. (After, Psuty, 1966) ...... 162

Figure 3.22 Dip-oriented stratigraphie section through the Nayarit strandplain. (After Curray et al, 1969) ...... 163

Figure 3.23 Schematic diagram depicting deposition of facies D and E within Lockhart Crossing field ...... 166

Figure 3.24 Frequency of occurrence and thickness of tempestites from the transition zone facies of the shoreface sequence from the unstable region of the margin ...... 168

Figure 4.1 Calculated shoreline positions from the Upper Cretaceous through Miocene based on Pitman's data for global sea-level fall. (See Fig.4.2). (After Pitman, 1978) ...... 189

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 4.2 Global sea-level curve, upper Cretaceous through .Miocene, based on spreading rates of mid-oceanic ridge system. The stippled area depicts the approximate time interval of Wilcox deposition. (Modified after Pitman, 1978) ...... 190

Figure 4.3 Stratigraphie relationships of the Wilcox supersequence within central Louisiana. Each sequence represents approximately 106 years. For most of Wilcox deposition, progradation did not bypass the Cretaceous shelf-margin ...... 192

Figure 4.4 Comparison of computed Tertiary sequence boundaries presented by Pitman (1978) (d-g) with those computed by STRATSIM (a-c). Note the differences in horizontal and vertical scales ...... 197

Figure 4.5 Linear regression of computed shoreline positions from the sequences shown in Figure 4.4 (d-g) with those in Figure 4.4 (a-c)...... 198

Figure 4.6 Sequence boundaries, sea-level curves, and shoreline shifts for the computed Tertiary sequences using program STRATSIM and assuming first-order global sea-level cycles. a) 150 million years wavelength: 250 m amplitude b) 200 million years wavelength: 250 m amplitude c) 250 million years wavelength: 250 m amplitude d) 250 million years wavelength: 200 m amplitude e) 250 million years wavelength: 275 m amplitude ...... 201

Figure 4.7 Computed Tertiary sequence boundaries and shoreline shifts using a first-order global sea-level cycle with a 250 million years wavelength and 275 m amplitude and variable second-order cycles. a) Second-order cycle: 100 million years wavelength -100 m amplitude b) Second-order cycle: 10 million years wavelength -100 m amplitude c) Second-order cycle: 50 million years wavelength -100 m amplitude d) Second-order cycle: 50 million years wavelength - 25 m amplitude ...... 204

Figure 4.8 Computed Wilcox sequence boundaries and shoreline shifts using a combination of first, second (see Fig. 4.7d), and third-order global sea-level cycles. a) Third-order cycle: 10 million years wavelength - 100 m amplitude b) Third-order cycle: 5 million years wavelength - 100 m amplitude c) Third-order cycle: 1 million year waveiength - 100 m amplitude ...... 208

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 4.9 Computed Wilcox sequence boundaries and shoreline shifts using a combination of first, second (see Fig. 4.7d) and third order global sea-level cycles. a) Third-ord cycle: 1 million year wavelength - 50 m amplitude b) Third-ord cycle: 1 million year wavelength - 25 m amplitude c) Third-ord cycle: 1 miilion year wavelength - 10 m amplitude d) Third-ord cycle: 1 million year wavelength - 5 m amplitude ...... 211

Figure 4.10 Hypothetical falling sea-level curves for the period of Wilcox deposition. SL=sea-level fall in cm per year a) SL1= 0.001 cm per year (1 cm/ lOOOyears) SL2= 0.0003 cm per year (0.3 cm/ lOOOyears) 106 year increments b) SL1 = 0.0005 cm per year (0.5 cm /10OOyears) SL2= 0.00065 cm per year (0.65 cm /10OOyears) 106 year increments c) SL1= 0.0002 cm per year (0.2 cm/ lOOOyears) SL2= 0.0014 cm per year (1.4 cm /10OOyears) 106 year increments d) SL1= 0 cm per year SL2= 0.0016 cm per year (1.6 cm/ lOOOyears) 106 year increments e) SL1= 0.001 cm per year (1 cm/ lOOOyears) SL2= 0.0003 cm per year (0.3 cm /10OOyears) 0.5 x106 year increments f) SL1= 0.0005 cm per year (0.5 cm/ lOOOyears) SL2= 0.00065 cm per year (0.65 cm/ lOOOyears) 0.5 x106 year increments g) SL1= 0.0002 cm per year (0.2 cm/ lOOOyears) SL2= 0.0014 cm per year (1.4 cm /10OOyears) 0.5 x106 year increments h) SL1= 0 cm per year SL2= 0.0016 cm per year (1.6 cm /10OOyears) 0.5 x106 year increments...... 214

Figure 4.11 Computed sequence boundaries and shoreline shifts assuming a variable rate of sea-level fall using the sea-level curves shown in Figure 4.10 a, b, c, and d ...... 215

Figure 4.12 Computed sequence boundaries and shoreline shifts assuming a variable rate of sea-level fall using the sea-level curves in Figure 4.10 e, f, g, and h ...... 218

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 4.13 Conceptual model of shoreface and transition zone facies. (After Aigner, 1985) ...... 223

Figure 4.14 Comparison of shoreface sequences from two shelf-margin sandstone bodies. a) Sun N. Smith, Jr. #8 core from Fordoche field (unstable shelf-margin). b) Sun Crown Zellerbach #1 from Lockhart Crossing/Livingston field (stable shelf-margin).In the vertical profile from the unstable margin, tempestites underlying the main shoreface are thicker (amalgamated) and exhibit a greater degree of bioturbation than those from the stable margin sequence ...... 224

Figure 4.15 Schematic of block structure used in the DEPSIM program. The shelf profile is defined by the midpoint of each block. Varying the thickness of each block enables simulation of changes in profile geometry ...... 226

Figure 4.16 Schematic cross-section through a modern beach shelf profile. (After Reineck and Singh, 1980) ...... 228

Figure 4.17 Simulated progradational shoreface sequence formed during a relative sea-level fall. a) Shoreface after 10 years simulation. b) Shoreface after 100 years simulation. c) Shoreface after 750 years simulation. d)Shoreface after 750 years simulation with subaerial erosion of exposed facies ...... 233

Figure 4.18 Comparison of progradational shoreface sequences which formed under variable rates of sea-level rise. a) shoreface sequence for a sea-level rise of 0.1 mm y ri b) shoreface sequence for a sea-level rise of 1.2 mm y ri c) shoreface sequence for a sea-level rise of 5.0 mm yr"* 236

Figure 4.19 Comparison of progradational shoreface sequences which formed during a sea-level rise, sea-level stillstand, and sea- level fall...... 239

Figure 4.20 Frequency of occurrence and intensity (0-3; O=lowest intensity) of simulated storms depicted in Figure 4.19 ...... 240

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 4.21 Close-up views of the transition facies of each of the shoreface sequences shown in Figure 4.19. a) rising sea-level b) sea-!evel stillstand c) falling sea-level ...... 242

Figure 4.22 Comparison of vertical profiles through the transition zones shown in Figure 4.21. a) rising sea-level b) sea-level stillstand c) falling sea-level Note that the number of tempestites, thickness, and potential for amalgamation are much greater in the rising sea-levei model (a) than in the falling sea-level model (c) ...... 244

Figure 4.23 Conceptual model for progradation and preservation of a truncated regressive shoreface which formed during a falling sea-level...... 247

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT

A strike-oriented trend of Wilcox oil and gas production in central Louisiana marks the location of an early Tertiary clastic shelf-margin. The shelf- margin contained a central unstable region flanked by two stable regions. The stable regions occurred where there was no significant progradation beyond the location of the underlying shelf-margins. Conversely, the unstable region occurred where progradation extended basin ward of the underlying shelf- margins. Seven depositional sequences can be recognized within the shelf- margin. The vertical arrangement of these sequences shows that migration of the margin was negligible throughout Wilcox deposition, thereby suggesting a balance between subsidence and deposition.

Through numerical simulation, it was concluded that published values for global cyclic sea-level fluctuations cannot be used to account for the development of these sequences. Rather, a sea-level which experiences variable rates of fall over a 0.5 x 10® year interval could account for the origin of such sequences.

A shale-filled submarine canyon system occurs within the unstable region of the margin. Morphologically, the canyon cross-sectional profile resembles that of an entrenched fluvial system. Conventional cores through sandstone bodies from stable and unstable regions of the margin exhibit similarities in vertical sequence and interval thickness. Both sandstone bodies represent truncated progradational shoreface sequences v/hich were associated with shelf-margin deltas. A computer program (DEPSIM) was developed in order to account for a significant difference observed between transition zone facies of the two

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. shoreface sequences. The shoreface sequence from the unstable region of the margin contains a well-developed transition zone facies in contrast to that from the stable margin. Results from the program suggest that the difference betv/een these two sequences may be explained by the fact that the sequence from the unstable region of the margin formed during a relative sea-level rise. The shoreface sequence from the stable region formed in response to a falling sea- level which resulted in extensive lateral translation of the shoreline. A vertical profile through the simulated shoreface sequence which formed during a sea- level fall therefore exhibits a poorly developed transition zone facies.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION

The shelf-edge represents an important geomorphic, tectonic, oceanographic and écologie boundary on the continental margins around the world (Stanley and Swift, 1976; Stanley and Moore, 1983). The shelf-edge is defined as the point at which there is a major change in gradient at the outermost extent of the continental shelf (Vanney and Stanley, 1983). Winker (1984) has suggested that the term 'shelf-margin' is more appropriate when examining the depositional features associated with the shelf-edge since it defines a broad geomorphic zone encompassing several distinct depositional systems rather than a single localized change in slope. For the purposes of this dissertation, the shelf-margin is defined in the terminology of Winker (1984) as a 'transition zone from shallow water deposition, dominated by wave, tide, storm, and rivermouth sediment transport, to deep water deposition dominated by gravity driven sediment transport (density flows, slides, slumps, etc.)'.

The character of the shelf-margin is a function of the general tectonic setting of the continental-margin, sea-level changes and sediment supply (Vanney and Stanley, 1983). Shelf-margins therefore exhibit a myriad of sedimentologic and structural characteristics. Seven broad categories of shelf-margin characteristics can be identified. These characteristics are as follows: 1) carbonate-dominated, 2) elastic-dominated, 3) retrogradational, 4) aggradational, 5) progradational, 6) structurally stable (limted occurrence of faulting), and 7) structurally unstable (Mougenot et al, 1983; Winker, 1984). An individual shelf-margin may exhibit some or all of these characteristics; spatially as well as temporally. From a stratigraphie viewpoint, the location and character of the shelf-margin has a significant influence on the facies

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architecture of depositional sequences which form on passive continental margins through geologic time.

This dissertation examines the stratigraphie framework and sedimentary facies of an ancient (Paleocene-Eocene) progradational clastic shelf-margin at three contrasting levels. At the first level, the regional characteristics of the shelf-margin are examined in terms of the component depositional sequences and structural stability. On a local scale, the second level examines the sedimentologic attributes and facies sequences of depositional features which occur at the shelf-margin through reference to conventional cores. The third and final level involves the numerical simulation of geological processes and their stratigraphie response at both the regional (depositional sequence) and local (depositional event) scale.

The study area is located in central Louisiana coincident with approximate locations of Cretaceous and early Tertiary shelf-edges (Hardin, 1962; Woodbury et al, 1973; Gaughey, 1975; McGookey, 1975; Martin, 1978). The dissertation is presented as four chapters intended for publication as separate papers.

The first chapter, 'Stratigraphie and structural framework of an ancient clastic shelf-margin; The Wilcox Group (Paleocene-Eocene), Central Louisiana', provides a regional perspective of the study area and a characterization of the shelf-margin. The Wilcox shelf-margin in Louisiana consists of at least three distinct regions of structural stability. A shale-filled submarine canyon occurs within the unstable region and appears to be a stratigraphie equivalent of the Yoakum channel (another shale-filled Wilcox submarine canyon system in Texas). Up to seven depositional sequences can be recognized in the stable region of the shelf-margin (W-l through W-VII, with W-l representing the oldest sequence).

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The second chapter, 'Sedimentary facies of the uppermost Wilcox shelf- margin trend: South Central Louisiana', has been published in T. F. Moslow and E. G. Rhodes, eds., Modern and Ancient Shelf Clastics: A Core Workshop, Soc. Econ. Paleontologists Mineralogists Core Workshop No. 9, p. 363-412. This chapter examines the sedimentary facies sequence of a sandstone body (within the W-VI sequence) which formed within the unstable portion of the shelf margin.

The third chapter, 'Recognition and character of a truncated regressive shoreface which formed during a sea-level fall', examines a facies sequence associated with another shelf-margin sandstone body (within the W-VII sequence) which occurs within the stable region of the margin. The interpretation of this facies sequence presented in this dissertation is in contrast to that which was presented in a previously published paper (Self et al, 1986). This facies sequence from the stable region of the margin is compared to that from the unstable region which is presented in Chapter two. The fourth chapter, 'Numerical simulation of depositional sequences and shoreface sequences from a clastic shelf-margin', examines two important concepts that were discussed in the previous chapters. The first concept concerns the origin cf depositional sequences on the Wilcox shelf-margin (discussed in Chapter one). Through the development of a computer program (STRATSIM) which simulates the formation of depositional sequence boundaries on a shelf-margin, it has been possible to examine the sequence stratigraphy which would result from cyclic fluctuations in eustatic sea-level as proposed by Vail et al (1977). The second concept concerns the differences between the two shoreface sequences which were presented in chapters two and three. Using another computer program (DEPSIM) developed by this author, it is possible to account for the differences in the appearance of these

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two sequences. Results from the simulations of the second computer program (DEPSIM) indicate that the shoreface sequence from the unstable region of the margin (Chapter two) formed during a relative sea-level rise as opposed to that from the stable region (Chapter three) which formed during a relative sea-level fall. Current facies models for prograding shoreface sequences are based on modern examples, all of which formed during a global sea-level rise (Bernard et al, 1962; Reineck and Singh, 1971; Howard and Reineck, 1981). DEPSIM enables the detailed characterization of facies sequences for a prograding shoreface which formed during a sea-ievel fall.

These four chapters are collectively intended to present an example of the stratigraphie and sedimentologic character of a progradational clastic shelf- margin. The methods utilized in this dissertation encompass conventional regional stratigraphie and local facies analyses in addition to the less commonly employed numerical simulation of geologic processes. Integration of these methods has enabled the characterization of a specific depositional setting in addition to the testing and development of some fundamental stratigraphie and sedimentologic concepts.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER I

STRATIGRAPHIC AND STRUCTURAL FRAMEWORK OF AN ANCIENT CLASTIC SHELF-MARGIN: THE WILCOX GROUP (PALEOCENE-EOCENE), CENTRAL LOUISIANA

ABSTRACT

The subsurface component of the Wilcox Group (Paleocene-Eocene) within Louisiana exhibits two well-defined trends of oil and gas production. One trend is located in the 'shallow' subsurface (900 to 1800 m: 2953 to 5905 ft) which is in the area that has been the subject of the majority of previous Wilcox studies. The second production trend is located downdip from the first trend and is coincident with the approximate location of early Cretaceous and early Tertiary shelf-margins. The section of the Wilcox which corresponds with the location of this downdip trend is an example of an early Tertiary shelf-margin. Up to seven low-order depositional sequences can be recognized in the

Wilcox shelf-margin trend. These sequences are bounded by regionally extensive shale horizons. The vertical succession of sequences reflects an apparent balance between basin subsidence and deposition throughout the period of Wilcox deposition. Basinward migration of the shelf-margin during Wilcox deposition therefore was relatively minor. The Wilcox shelf-margin exhibits three regions of structural stability. Two of the regions are located in western and eastern central Louisiana and exhibit relatively stable shelf-margins as manifested by the minimal occurrence of

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. syndepositional-faulting (growth-faulting). Between these two stable regions, the shelf-margin appears structurally unstable due to the preponderance of large-scale growth-faults. The stable shelf-margin regions occur where Wilcox sediments did not prograde significantly beyond the previous maximum advance (Tuscaioosa sheif-margin).

A thick shale interval which was believed by previous workers to represent the occurrence of a major marine transgression midway through Wilcox deposition is not readily apparent on regional well-log cross-sections. However, localized thickening of this interval is apparent within the Wilcox shelf- margin. The discordant relationship with underiying strata and a channelized form suggests a period of extensive downcutting occurred during the middle Wilcox. The feature is almost 24 km (15 mi) wide and up to 300 m (984 ft) thick and is interpreted to have formed close to the shelf-margin by fluvial downcutting during a sea-level lowstand. There potentially exists new, deep, (4,600-6,000 m : 15,000 - 20,000 ft) hydrocarbon exploration targets in the iow- stand system tracts associated with the formation of this feature.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION

The Wilcox Group (Paleocene-Eocene) is a thick (up to 1,220 m; 4,000 ft) sequence of clastic sedimentary rocks which represent the initial progradational phase of Tertiary sediments into the Gulf of Mexico basin. In Louisiana, the Wilcox is almost exclusively confined to the subsurface. Most previous studies have focused on the 'shallow' intervals of the Group (Galloway, 1968; Herbert, 1972; Coates, 1979; Mabibi, 1979; Coates et al, 1980; Cleaves and O'Neill, 1983; Rogers, 1983, and Purcell et al 1985). The term 'shallow' has been used to signify the relatively shallow subsea depth of the Wilcox interval (900 to 1,800 m: 2,900 to 5,900 ft). A well defined dip-oriented trend of oil and gas production occurs within the shallow Wilcox (Fig. 1.1) and is believed to represent fluvial- dominated deltaic and alluvial plain sandstone reservoirs (Craft, 1966). Downdip from the 'shallow Wilcox', a second trend of oil and gas fields extends along strike through central Louisiana (Fig. 1.1). The average subsea depth of the top of the Wilcox in this region is between 3,000 to 4,200 m (9,800 to 13,800 ft).

The location of the strike-oriented production trend is in close proximity to lower Cretaceous and Eocene shelf-margins (Hardin, 1962; Woodbury et al, 1973; Caughey, 1975 a; Caughey, 1975 b; McGookey, 1975; Martin, 1978) (Fig. 1.2). The term shelf-margin, as it is used in this dissertation, was defined by Winker (1984) as: 'the transition zone from shallow water deposition dominated by wave, tide, storm and river mouth sediment transport, to deep water deposition dominated by gravity driven sediment transport (density flows, slides, slumps, etc.)'. The purposes of this chapter are: 1) to establish the general stratigraphie and structural framework of the Wilcox Group within this downdip

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region, and 2) to examine the influence of pre-existing shelf-margins on the stratigraphie development of the Wilcox shelf-margin. This chapter will first provide a synopsis of the geologic framev/ork of the regional study area followed by a more specific review of the depositional history of the Wilcox Group as it is currently reported in the literature. A revised classification of the Wilcox in Louisiana based on low-order depositional sequences will then be presented. The following aspects of the shelf-margin will then be discussed: 1 ) the structural stability of the margin, and 2) the occurrence of a submarine canyon system within the shelf-margin.

GEOLOGIC BACKGROUND

Pre-Wilcox Stratioraphv

Throughout the early Cretaceous (Berriasian through Albian; 144-97.5 ma), a series of carbonate reef systems circumscribed the northern rim of the Gulf of Mexico basin (Hendricks and Wilson, 1967; McFarlan, 1977) (Fig. 1.3). The existence of these reef systems resulted in the formation of successive stable continental shelf-margins through the area of central Louisiana during this time period (Adams, 1985). The position of these shelf-margins remained within a relatively narrow zone (30 to 50 km: 19 to 30 mi) until the beginning of the late Cretaceous (Cenomanian; 97.5 ma). At this time, shallow marine and deltaic sediments of the Tuscaloosa formation were deposited close to and beyond the Edwards reef trend (Smith, 1981 ;1985) in asponse to a major relative sea-level fall (Vail et al, 1977). This was a period of extensive marginal basin-filling as sediments derived from fluvial and submarine canyon systems formed thick (500 to 600 m: 1,600 to 2,000 ft) sequences of deep-water deposits

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CD ■ D O Q. C g Q.

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BA8M RESEARCH MSTITUrE ■D L0U8IAHA STATE UNIVERSITY CD (/) Figure 1.1 Generalized structure contour map of the top of the Wilcox Group in (/> Louisiana. Note the location of two well-defined oil and gas production trends. The shallow Wilcox trend in LaSalle, Concordia and Catahoula Parishes is primarily dip-oriented. The deep Wilcox extends through Livingston, East Baton Rouge, Pointe Coupee and (O Beauregard Parishes. 10

AAfAS Of MAJOR LOUISIANA CINOfCNC SEOlMENTAfiON AlABAMA MiSSiSSiPP ^tiitoont and Lart M'ocene nofiiPA

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Figure 1.2 General location of early Cretaceous and Tertiary shelf-edges within the northern rim of the Gulf of Mexico basin. (After Martin, 1978).

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basinward of the reef trend (Berg, 1982) (Fig. 1.4). This progradational episode resulted in the migration of the shelf-margin up to 30 km (20 mi) in places beyond the reef trend (Harrison, 1980).

As relative sea-level began to rise again (Vail et ai, 1977), pelagic and hemipelagic muds onlapped against the Tuscaloosa shelf-margin. Continued sea-level rise up to the late Cretaceous (Maestrichtian; 74.5 to 66.4 ma) highstand resulted in the formation of extensive chalk sequences (Granada, 1963). By the end of the Cretaceous (-66.4 ma), relative sea-level began to fall again which resulted in progradation of Tertiary clastic sequences. In central Louisiana, the incipient stages of this progradation are represented by deep water facies of the (Paleocene) and the overlying shallow- marine and fluvial-deltaic sediments of the Wilcox Group (Paleocene-Eocene) (Howe, 1962; Dixon, 1965).

Wilcox stratioraphv

Early geologic investigations of the Wilcox Group in Louisiana were primarily concerned with recognition and description of individual formations at limited surface exposures (Murray and Thomas, 1945; Murray, 1948; and Andersen, 1960). However, subsequent studies had limited success in trying to correlate these formations to the subsurface Wilcox section (Smithwick, 1954 and Dixon, 1965).

Results from later studies of the subsurface Wilcox in Louisiana (Galloway, 1968; Coates et al, 1980; Rogers, 1983, and Purcell et al 1985) agreed with those from the Texas Wilcox studies (Fisher and McGowen,1967). Fisher and McGowen (1967) showed that the subsurface Wilcox in Texas was comprised of three major divisions (Fig. 1.5). These divisions were recognized

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Oc % Figure 1.3 Schematic dip cross-section through early Cretaceous shelf- margins from the northern rim of the Gulf of Mexico basin. This (/)eg o ' profile is located in south Texas; however, the broad stratigraphie 3 relationships are similar along the shelf-margin. (After Hendricks and Wilson, 1967). ro CD ■ D O Q. C g Q.

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on the basis of electric log character. Interpretation of the depositional history of each division is as follows:

Lower Wilcox

In Texas, Fisher and McGowen (1967) recognized the Lower Wilcox interval as representing an important phase of delta construction exemplified by the Rockdale delta complex. In Louisiana, large deltaic complexes began to encroach into the area as sediment supply increased and/or basin subsidence decreased relative to eustatic sea-level fall. Galloway (1968) recognized that the Holly Springs delta complex (Fig. 1.6) was the Louisiana stratigraphie equivalent of the Rockdale complex. The Holly Springs delta complex formed within the drainage axis of the Mississippi embayment and, like the Rockdale delta, was considered to be fluvially-dominated.

Middle Wilcox

Overlying the fluvial-deitaic complexes of the Lower Wilcox is an interval of fine-grained, deep-water sediments which are believed to represent a major marine transgressive event. This interval (middle Wilcox) has been colloquially referred to as the 'Big shale' in Louisiana (Howe, 1962; Dixon, 1965). The interval has been used as a regional marker bed in numerous subsurface studies (Coates et al, 1980; Mulcahy, 1981; Rogers, 1983, and Purcell et al 1985).

Upper Vvilcox

The final phase in Wilcox depositional history is characterized by a major regressive sequence prior to initiation of the next major transgression of the Claiborne Group (Eocene). Sandstone bodies in this interval constitute the

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GENERALIZED WILCOX SUBSURFACE DIVISIONS

UPPER WILCOX WAVE DOMINATED

MIDDLE WILCOX MARINE TRANSGRESSION

LOWER WILCOX

DOMINATED

AFTER GALLOWAY, 1968

Figure 1.5 Schematic Wilcox subsurface divisions showing the fluvial- dominated lower Wilcox overlain by a major marine transgressive sequence (the 'Big Shale'). The upper Wilcox is believed to be composed of a series of wave-dominated deltaic complexes.

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majority of Wilcox hydrocarbon reservoirs in the shelf-margin trend. Unlike the dip-oriented trend in the Lower Wilcox, they are oriented parallel with depositional strike. These sandstone bodies formed at the furthest seaward migration of the shoreline during Wilcox time and are believed to represent wave-dominated delta systems (Galloway, 1968). Unfortunately, recognition of this threefold division in the Louisiana subsurface is a highly subjective process. A single 'Big shale' interval separating the Wilcox Group is not readily apparent on regional well-log cross-

sections. Rather, several shale intervals of comparable thickness can be observed within the downdip shelf-margin trend. Consequently, use of the threefold classification system was abandoned. Instead, a divisional characterization of the subsurface Wilcox based on low-order depositional sequences has been adopted. Recognition of these sequences provides a means by which to examine the large scale phases of basin-fill during Wilcox deposition.

DEPOSITIONAL SEQUENCES AND SEQUENCE STRATIGRAPHY

The sediments which fill the basin of a passive continental margin are comprised of numerous genetically-related lithologie units (sequences) bounded by unconformities (Vail et al, 1977; Hubbard et al, 1985 a; Sloss, 1984). These sequences may represent long term (10® years) phases of basin- filling (high-order sequences) or short term (103 to 1Q4 years) ephemeral depositional pulses (low-order sequences) (Miall, 1984). As the margin evolves through time, the superimposition of successive sequences occurs in response to allocyclic and autocyclic depositional and structural regimes. Seismic recognition of genetically-related packages bounded by regional

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m

Figure 1.6 Schematic diagram of the lower Wilcox Holly Springs deltaic complex in Louisiana and Mississippi. (After Galloway, 1968).

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unconformities has been widely used in large scale basin analyses performed mainly by major oil companies over the last decade (Berg and Woolverton, 1985). Hubbard et al (1985 b) provide an excellent example of this approach in case studies from continental margins off Newfoundland and the Beaufort Sea. The fundamentals of sequence stratigraphy gained prominence when Sloss (1963) proposed that six major Phanerozoic stratigraphie sequences could be recognized on the north American craton. The unconformities which bound each sequence are considered to be geologically significant since they formed in response to global tectonism. This type of sequence is an example of one level in the hierarchy of stratigraphie sequences and is comparable to the supersequence described by Vail et al, (1977). Frazier (1974) showed how the concept of geneticaily related depositional units could be applied to resoive the stratigraphie framework of an interval to a much finer level than that discussed by Sloss. Frazier introduced the concept of depositional complexes and facies sequences and demonstrated

how the modern Mississippi deltaic complex was comprised of a series of genetically-related packages. Within his definitions, he describes the depositional complex as: "... a series of conformable facies sequences bounded by regional hiatal surfaces', and a facies sequence as: ... an initial basinward progradation, penecontemporaneous and intermediate aggradation and is terminated by a local transgression' (Frazier,1974).

Figure 1.7 diagrammatically depicts Frazier's concepts. The duration of time within which the depositionai complex forms is termed a 'depositionai episode': and the duration of time during which a facies sequence develops is calied a 'depositional event' (Frazier,1974). Each facies sequence contains a spectrum of depositional environments from alluvial facies to the paralic and deep-marine. Recognition of these low-order depositional "signatures" using

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Figure 1.7 Definitions of depositional episodes and depositional events ■D CD according to Frazier. (After Frazier, 1974).

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well-log and conventional core data provides a platform from which one can develop an integration of seismic stratigraphie analyses on a basinwide scale with the components of individual sequences on a local scale.

RECOGNITION CRITERIA FOR DEPOSITIONAL SEQUENCE BOUNDARIES

Introduction

In the absence of extensive paléontologie and seismic data, recognition of individual depositional sequences within the subsurface using well-log cross- sections is based on the premise that the shale interval between two individual sequences was formed during a relative sea-level highstand. Forgotson (1957) recognized the importance of thick shale horizons in enabling geologists to subdivide terrigenous clastic sequences in the subsurface into discrete 'transgressive and regressive couplets’. Forgotson pointed out that at the outcrop recognition of a "sandy conglomeratic, fossiliferrous layer, with an abundance of authigenic minerals such as glauconite’ is the common means to separate the transgressive regressive couplets. However since recognition of these units on electric logs is relatively limited, he emphasized that the most reliable markers in the subsurface are 'thick' regionally-extensive shale units which were assumed to be deposited during a relative sea-level highstand.

At least six such shale intervals (A through F) can be recognized within the Wilcox of central Louisiana (Fig. 1.8). On well-log cross-sections, these shale intervals are laterally continuous and moderately thick (15-25 m: 50-80 ft). The interval commonly referred to as the 'Big shale' is no thicker than any of the other shale intervals in this area; however, local thickening of this shale does

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Figure 1.8 Regional strike-oriented weil-iog cross-section showing ■D depositional sequences (W-1 through W-V11) and major CD transgressive shale units (A-F) within the Wilcox of central

C/) Louisiana. The upper boundary of each sequence Is defined by a C/) regional transgressive disconformity. (See #4 on Fig. 1.17 for location of cross-section). 22

occur. Each of these shale Intervals exhibit characteristic attributes which may be considered as simple recognition criteria for depositional sequence boundaries.

Recognition criteria

Lateral continuity and fades relationships

Three of the six shale intervals (D, E and F) within the central Louisiana subsurface can be traced along depositional strike over 160 km (100 mi) (Fig. 1.8). Three other shale intervals (A, B and C), evident in the eastern region, become progressively more difficult to identify towards the west. This apparent lack of lateral continuity of the lower shale horizons may be due to the fact that this strike profile is located close to the maximum landward limit of early Wilcox transgressions. The lack of continuity may also be due to the fact that the area where the shale intervals become progressively more difficult to recognize corresponds with a region of major growth-faulting. Growth-faulting may have the effect of obscuring the regional shale intervals. Figure 1.9 shows these same shale intervals extending up to 112 km (70 mi) in the dip direction. Updip, the shale intervals rapidly pinch out into a predominantly sandier component of the section. Downdip, these shales merge into basinal facies.

Marine Fauna

Benthic foraminifera which occur within several of these shale intervals represent paleoecological zones which range from middle neritic (15 to 90 m: 50 to 300 ft) to lower bathyal (460 to 1800 m: 1500 to 6000 ft) (Table 1.1).

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of Wilcox

WILCOX

DWAY I ^ Î UPPER CRETACEOUS c CHALKS

Tuscaloosa

Lower Cretaceous sheK edge 3

1 0 0 0 ft.

Figure 1.9 Regional dip-oriented cross-section showing Wilcox depositional sequences and their relationship to the early Cretaceous reef trend and Tuscaloosa shelf-margin in central Louisiana. (See #2 on Fig. 1.17 for location of cross-section).

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FAUNA ENVIRONMENT

Ciblcldes sp. Middle she!f-!ower slope Haplophragmoides sp. Lower slope Uvigerina sp. Middle she If-Abyssal Robulus sp. Middle shelf-Upper slope

Table 1.1 Benthic foraminifera from shale interval F.

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Nature of the lower contact

By definition, a depositional sequence is bounded by an unconformity or its correlative conformity (Vail et al, 1977). It is tfierefore essential that an unconformity should be established between the shale and the underlying facies in order to consider the shale intervals to have formed during a relative sea-level highstand. This contact can be recognized in conventional cores. In Chapter two, a vertical profile from a facies sequence which underlies one of the regional shale intervals (E) depicts a progradational shoreface truncated by erosional shoreface retreat. Erosional shoreface retreat resulted in the creation of a well-defined ravinement surface (Swift, 1968). The ravinement surface is a time-transgressive boundary which defines the hiatal contact referred to by Frazier (1974). In some cases, a thin (0.5 m; 1.6 ft) calcarenite occurs at the ravinement surface and appears as a strong positive deflection on the resistivity log (see Chapter two). Significant relative sea-level highstands may be distinguished from local transgressions on the basis of lateral continuity of the shale intervals. Laterally continuous shale intervals represent a significant relative sea-level highstand and are moderately thick (15-25 m; 50-80 ft). Relatively thin (2 to 5 m: 6.5 to 16.0 ft) and laterally discontinuous mudstones overlying the ravinement surface represent a local transgression which occurred prior to the progradation of the subsequent depositional event.

WILCOX DEPOSITIONAL SEQUENCES

Up to seven depositional sequences (with W-l representing the oldest and W-VII the youngest) can be recognized from the regional well-log cross-

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sections throughout the study area. These sequences can be easily distinguished on a regional strike-oriented well-log cross-section which extends through township 2-8 (Fig, 1.8) and on a dip-oriented cross-section from the eastern region of the study area (Fig. 1.9). Resolution of sequences W-l, W-ll, W- III and W-IV on the well-log cross-sections becomes more difficult towards the western part of the study area.

Exact age ranges for these sequences cannot be established at this time due to a lack of paleontological data. However, on the basis of the number of sequences which formed within the time interval of Wilcox deposition (107 years) these sequences may be considered to be equivalents of the third or fourth order sequences described by Vail et al (1977). Variation in the basin ward extent of the main arenaceous component of sequences W-l through W-VI was relatively minor (less than 8 km: 5 mi). On the other hand, the final Wilcox sequence (W-VII) exhibited the greatest basinward progradation of the arenaceous component. The general arrangement of the Wilcox sequences (i.e. relatively minor progradation from the initial basinward limit) reflects a history of basin-filling where the rate of subsidence has approximated the rate of deposition (Fig. 1.10). Vail et al (1977) have suggested that the Wilcox in Texas reflects a balance between basin subsidence, sediment supply and sea-level fluctuation such that a seismic section would reveal a predominance of toplapping sequence boundaries .

This interpreted sea-level history for Wilcox deposition differs from the previous interpretation (Galloway, 1968; Coates et al, 1980; Rogers, 1983, and Purcell et al 1985). In recognizing these depositional sequences, it has become apparent that the shale interval commonly considered to have formed during a major Wilcox marine transgression (the 'Big shale') is only one of at least six other equally thick sequences which formed during Wilcox deposition.

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SEA-LEVEL

V r_ >1

SEA-LEVEL

SEA-LEVEL

ALLUVIAL*. FLUVIAL-DELTAIC □ SANDS AND SILTS DELTAIC SANDS, SILTS IlMmi!##!! & CLAVS

PRODELTAIC AND MARINE CLAYS

Figure 1.10 .Schematic diagram showing inferred facies relationships which result from differences between subsidence and deposition. The Wilcox sequences shown in Figure 1.9 most closely approximate the condition shown in part b. (Modified after Curtis, 1970).

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WILCOX SHELF-MARGIN STABILITY

Several factors may exert a significant influence on the stratigraphie character of a shelf-margin. These factors include eustatic sea-level change, sediment supply, tectonism, and the stability of the margin. Winker (1984) recognized three major categories of progradational clastic shelf-margins in the Gulf Coast based on the overall stability of the margin (Fig. 1.11). Each shelf- margin has a relatively unique stratigraphie framework which is primarily controlled by the margin stability. Shelf-margins in the Wilcox are frequently cited as examples of unstable prograding clastic margins (Edwards, 1981; Winker, 1982,1984; Winker and Edwards, 1983). However, it is evident that a modern clastic shelf-margin may exhibit spatial variability of these three major stability regimes (Martin and Bouma, 1978, Martin, 1978).

The purpose of this section is to examine the temporal and spatial variability of the stability of the Wilcox shelf-margin and its resultant effect on the stratigraphie framework of the margin. In the absence of regional seismic data, a series of pseudolithologic dip-oriented profiles (Fig. 1.12, 1.13, 1.14) were constructed using spontaneous potential (SP) logs to help identify large scale growth-faulting. The profiles were constructed by first determining sandstone percentage at 32.8 m (100 ft) intervals for each of the cross-sections. These data were then contoured using a contour interval of ten percent. Figure 1.12 is a contour diagram of sandstone percentage of a dip cross- section in the easternmost region of the study area (Livingston Parish). There are two important aspects depicted in this diagram. The first aspect concerns the appearance of at least three major phases of progradation (1, 2 and 3).

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Figure 1,11 Schematic diagram depicting major categories of clastic shelf- margins within the Gulf of Mexico basin. (After Winker, 1984).

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% (gC/) SANDSTONE PERCENTAGE: EASTERN DIP PROFILE 3o ' NORTH SOUTH CD Depth in Feet MS I LA 8 r O I— cB' '1000 3 CD -2000 C 20% ------p. 3" -60% CD '3 0 0 0

CD 0% --- ■o 10 miles IC a o 3 ■o o Figure 1.12 Dip-oriented sandstone percentage profile through the Wilcox in central Louisiana. (See #1 on Fig. 1.17 for location). &

%

(gC/) o ' 3

CO o ■o o Q. C 8 a .

■o CD c/) (fi SANDSTONE PERCENTAGE: CENTRAL DIP PROFILE SOUTH north Depth in feet CD 8

ë '

3 CD

C p.

■OCD O Q. C a O3 10 miles O 3*

CD Q.

Figure 1.13 Dip-oriented sandstone percentage profile through the Wilcox in TD central Louisiana. (See #2 on Fig. 1.17 for location). CD (/) o ' 3 w 73 ■DCD O Q. C g Q.

■D CD

C /) C /) SANDSTONE PERCENTAGE : WESTERN DIP PROFILE

NORTH SOUTH ■D8 (O' Depth in Feet M Sj LA

-1000 3"3. CD ■DCD O -2000 Q. C a go 3O "O - 3 0 0 0 O

20

CD Q. 10 miles

T3 CD

C /i Figure 1.14 Dip-oriented sandstone percentage profile through the Wilcox in C/i central Louisiana. (See #3 on Fig. 1.17 for location).

COro ■OCD O Q. C 8 Q.

■O CD

WC /) o"3 COASTAL PLAIN CONTINENTAL SHELF SLOPE O 3 CD "O8

(O'

Z-33 U0W-DENSITYI-3-I-2-Z-I-: TEXAS COASTAL AREA HIGH-PRESSURE s h a l e -5 5 ; 3. 3" CD HOUSTONB PRE-TERTIARY SECTION "OCD O Q. C CORPUS Oa c h h i s t i 3 "O O U ILE 5

CD Q.

Figure 1.15 Generalized lithologie cross-sectIon through the Tertiary of the ■D CD Texas coastal plain showing large-scale growth-faulting. Compare this figure with that depicted In Figure 1.14. (/)

w CO 34

Initial progradation (1) extended almost as far basinward as the final phase of progradation (3); however, the intermediate phase (2) did not extend as far basinward ,= the initial (1) and final (3) phases. The second important aspect of the profile concerns the relatively horizontal nature of the contour lines which signifies that there was little or no syndepositional downdip thickening of the section. In figure 1.13, the profile extending through East Baton Rouge Parish which lies 48 km (30 mi) to the west of the profile shown in figure 1.12 shows a similar pattern of depositional phases with minimal structural modification. Further west, in Pointe Coupee Parish, the character of the shelf-margin differs dramatically from that depicted in figures 1.12 and 1.13 (Fig. 1.14). This profile (Fig. 1.14) reveals the occurrence of significant syndepositional dov/ndip thickening of the Wilcox section. Bruce (1973) presented a profile for the Tertiary sequence of the Texas Gulf Coast (Fig. 1.15) similar to that depicted in figure 1.14. Despite the apparent dramatic structural deformation in the Pointe Coupee region of the shelf-margin, it is still possible to recognize three major progradational pulses. Further to the west, near the Texas state line, the character of the margin has changed again. A reflection seismic line in this area (Fig. 1.16) suggests that the Wilcox shelf-margin is similar to the stable shelf-margin in the eastern region of the study area. The stable nature of the shelf-margin is exemplified by the occurrence of relatively undeformed sigmoidal clinoforms (Fig. 1.16). In contrast to this lack of structural activity, it is evident that the underlying Tuscaloosa shelf-margin has been extensively growth-faulted. Like the eastern region, there was relatively little migration of the margin throughout Wilcox deposition. Figure 1.17 is a schematic representation of the spatial variation in Wilcox shelf margin stability through central Louisiana.

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Of the factors (outlined above) which may affect the stability of shelf- margins, sea-level change and regional tectonism can be eliminated as potential causes of the spatial variability along the Wilcox sheif-margin. The position and stability of pre-existing margins appear to exert the greatest influence on the stability of the Wilcox shelf-margin. It becomes clear from the regional well-log cross-section (Fig. 1.10) and seismic line (Fig. 1.16) that the basinward limit of the Wilcox shelf-margin in the eastern and western regions of the state did not extend significantly beyond the location of the underlying Cretaceous shelf-margins. The zone of greatest instability along the Wilcox shelf-margin corresponds to the region where Wilcox progradation extended beyond the location of the underlying margins (Fig. 1.17).

WILCOX SUBMARINE CANYON SYSTEM

General morphology and stratigraphie relationships

Figure 1.8 shows the occurrence of a thick feature within the unstable portion of the Wilcox shelf-margin. This zone of thickening roughly corresponds

to what other workers have called the Big Shale (shale interval E). The pattern of local thickening (Fig. 1.18) is identical to that which occurs in the Yoakum submarine canyon system (Hoyt, 1959) (Fig. 1.18). The area of thickening also corresponds with the approximate location of a Midway (Paleocene) submarine canyon in St. Landry Parish (Winker, 1984). There are no specific details concerning the exact location or morphological characteristics of the canyon in St. Landry Parish given in Winker's paper.

A series of well-log cross-sections reveal a channel profile that can be traced over at least 24 km (15 mi) along dip (Fig. 1.19). Downdip and updip from

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7) ■DCD O Q. C g D.

■O CD

C/) o ' Z5

8 cB'

3 CD

C 11,5000 ft. 3. Top of Wilcox 3" CD ■OCD IC 16,000 ft aO 3 Tuscaloosa ■a o Lower Cretaceous CD û . 5 miles shelf edge 3"O

■o CD Figure 1.16 Reflection seismic profile across the Wilcox and early Cretaceous C/) C/) shelf-margins from western-central Louisiana. Note the relatively undisturbed character of the Wilcox reflectors and relative positions of the Tuscaloosa and pre-Tuscaloosa lower Cretaceous shelf- edge. (See #6 on Fig. 1.17 for location of line). COo> 37

Figure 1.17 General map of central Louisiana showing relative positions and stability regimes of the Wilcox shelf-margin. It appears that the lower Cretaceous shelf-edge in western Louisiana is located downdip from the Edwards-Siigo Reef Trend. (Also see Berg, 1982). The central unstable region of the margin corresponds to the location where the Wilcox prograded significantly beyond the pre-existing margins. 1. Location of profile shown in Figure 1.12. 2. Location of profiles shown in Figure 1.9 and Figure 1.13. 3. Location of profile shown in Figure 1.14. 4. Location of profile shown in Figure 1.8. 5. Location of profile shown in Figure 1.20. 6. Location of profile shown in Figure 1.16.

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■D CD BASINWARD EXTENT OF SHELF-MARGINS WC /) REQONOF STABLE SHELFMARQNS 3o" WILCOX O TUSCALOOSA (llllllllillilllllll EDWARDS Arm 8 "D SLIGO REEF TREND (O'3" i 3 CD iiiiuiiui!!!.!;

3. 3" CD ■DCD O Q. C Oa 3 ■D O

CD Q.

LOUISIANA ■D CD 3 W(/) o"

C3 00 39

WEST STRIKE CROSS-SECTION THROUGH AVOYELLES/ST. LANDRY CANYON EAST

W-VI -

W-IV

B

STRIKE CROSS-SECTION THROUGH YOAKUM CHANNEL

'MOP' TOP OF WILCOX

UPPER MASSIVE 5 SANDS -n *

CHANNEL FILL

WjLCOX

*oco,

MILES AFTER HOYT, I9 S 9 ~

Figure 1.18 a) Strike-oriented well-log cross-section through localized thickening of shale inteval E. (See Fig. 1.8). b) Strike-oriented cross-section through the Yoakum channel system in the Wilcox of Texas. (After Hoyt, 1959).

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A'

TIS

-500 T2S

L- 1000 FT

5 MILES T3S

CANYON PROFILES IN AVOYELLES PARISH

Figure 1.19 Strike-oriented profile through the submarine canyon system in Avoyelles Parish. (See Fig. 1.17 for location).

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the location of these cross-sections, the outline of the channel becomes progressively more difficult to resolve. Downdip, the Wilcox section becomes increasingly argillaceous and the shale-filled channel is indistinguishable from the surrounding mudstones. Updip, the Wilcox section and the channel-fill become progressively arenaceous and, therefore, it is extremely difficult to detect the channel on well-log cross-sections. A strike-oriented reflection seismic line through the St. Landry Canyon system shows the relatively subtle nature of the relief (Fig. 1.20). The truncation of the underlying reflectors is clearly demonstrated as is the lateral continuity of the reflector which caps the channel sequence. Internal character in the lower portion of the fill is dominated by chaotic seismic facies. The sequence is overlain by gently dipping and relatively continuous reflectors. As noted above, similar shale-filled channels features occur elsewhere in the Gulf Coast Tertiary sequence (Bornhauser, 1948; Hoyt, 1959; Galloway and Brown, 1973; Vormelker, 1980; Chuber and Begeman, 1982; Jackson and Galloway, 1984). Several other ancient shale-filled submarine canyon sequences from a variety of shelf-margin settings located throughout the world have been reported in the literature (Cohen, 1976; Almgren, 1978; Picha, 1979; Clifton, 1981; May et al, 1983). One of the most renowned examples of a submarine canyon system in the Gulf coast Tertiary is the Yoakum channel, located in Yoakum County, Texas. The Yoakum channel formed during the Upper Wilcox (Hoyt, 1959).

The morphology of the Wilcox channel In central Louisiana, hereafter referred to as the St. Landry Canyon, differs significantly from that of the Yoakum Channel in the downdip region. Figure 1.21 compares canyon profiles from these two features. Total thickness of the Yoakum channel-fill is on the order of 610 m (2,000 ft) compared to only 300 m (984 ft) for the St. Landry

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Figure 1.20 Refisction seismic profiie through the üt. Landry Canyon. (See #5 on Fig. 1.17 for location).

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. f

If h

»

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COMPARISON OF YOAKUM AND AVOYELLES/ ST. LANDRY “ CANYON” PROFILES

YOAKUM 5 MILES

ST. LANDRY - 5 0 0

L 1000 FT

MODIFIED AFTER HOYT, 1959

Figure 1.21 Comparison of Avoyelles/St. Landry Canyon profile to Yoakum channel profile.

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Canyon. The St. Landry Canyon has a much broader channel geometry than the Yoakum and is up to 24 km (15 mi) wide in places compared to 8 to 16 km (5 to 10 mi) for the Yoakum. Both canyons are predominantly shale-filled; however, rare sandstone intervals occur within the St. Landry Canyon. It is possible that the difference in canyon morphology between the Yoakum and St. Landry systems is merely a manifestation of natural variability in these features. Figure 1.22 compares profiles from the Yoakum and St. Landry systems with profiles from some modern submarine canyon and fluvial systems. As a result of this comparison, it becomes evident that the profile geometry of the St. Landry Canyon and that of the entrenched alluvial valley of the Mississippi River are very similar.

Model of canvon development

Two general models exist to account for the development of submarine canyons. In the first model, Fisk and MacFarlan (1955), Shepard (1981), Steffens (1986) believe that canyons form in response to fluvial downcutting during a sea-level lowstand. The reduction in sea-level may be due to either

eustasy or regional tectonism at the continental margin. The second model proposes that mass wasting at the shelf-edge is the initial stimulus which triggers the formation of a canyon (Coleman et al, 1983; Bouma et al, 1984). Once the incipient phase of canyon development has occurred, retrogressive slumping results in the landward migration and progressive deepening of the canyon.

As shown previously, the St. Landry Canyon occurs within the most unstable region of the Wilcox shelf-margin. Similarly, the Yoakum channel occurs within an unstable region of the Texas Wilcox shelf-margin (see Jackson

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0 m ile s 10 Mississippi Canyon

M onterey Yoakum SOOOfeet

Grand Canyon Great Bahama

St. Landn

Mississippi Trench (near Donaldsonullle) ^

Data from Fisk and McFar!an,1955; Hoyt,1959; Shepard and Dill, 1966; Moore et al, 1978 and Coleman et al, 1983.

Figure 1.22 Comparison of St. Landry Canyon and Yoakum channel profiles with some modern canyon profiles.

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and Galloway, 1984). It Is therefore possible that Instabilities which arose from progradation beyond the previously existing margin resulted In the initiation of these two canyons. However, two lines of evidence suggest that the St. Landry Canyon may have formed as a result of fluvial downcutting which, in turn, occurs In response to an inter-reglona! relative sea-level lowstand. These lines of evidence are as follows: 1) The St. Landry Canyon formed at the end of deposition of sequence W-V and prior to deposition of sequence W-VI. The end of deposition or upper boundary of each sequence represents a relative sea- level lowstand. 2) Canyon systems of a similar age occur In Texas which suggests that a more regional process (I.e. sea-level lowstand) occurred. There are two Important Implications regarding this Interpretation. The first Implication Is that. In contrast to previous Interpretations of the Wilcox deposltlonal history, a major sea-level fall must have occurred during late- middle or upper Wilcox. The second Implication concerns the potential for deep- sea fan reservoirs to occur downdip from the canyon. However, the depth at which such a feature would occur (In excess of 4,500 m; 15,000 ft) must be considered when any attempts to exploit hydrocarbon reservoirs associated with a St. Landry deep-sea fan are made.

DISCUSSION

The Wilcox Group may be considered to be part of an early Tertiary supersequence according to the terminology of Vail et al (1977). This supersequence Includes sediments belonging to the Midway Group (Paleocene). At least seven deposltlonal (third order) sequences can be recognized In the Wilcox shelf-margin trend.

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Figure 1.23 shows a schematic sequence of events which led to the deposition of the Wiicox-Midway supersequence in Louisiana. This sequence is comprised of six major events. 1) A shelf-margin carbonate reef system

(Edwards Reef trend) occurred in the area of central Louisiana near the end of the early Cretaceous (Albian) (Fig. 1.23a). 2) A major relative sea-level fall occurred at the end of the Albian (Vail et ai, 1977) resulting in the transport of sediments beyond the shelf-margin which, in turn, resulted in the creation of the onlapping sequence shown in figure 1.23b. As pointed out earlier, this event was an important phase in basin development around the Gulf Coast Basin. Deposition of sediments beyond the stable carbonate shelf-margin provided the foundation for successive progradational episodes which would extend beyond the lower Cretaceous shelf-edge. 3) As sediment supply was maintained during the ensuing rise of sea-level, the third sequence (Tuscaloosa Formation) was deposited close to and beyond the shelf-edge (Fig. 1.23c). 4) The continued relative rise in sea-level is depicted in figure 1.23d. Baslnal mudstones followed by thick Upper Cretaceous chalk sequences were deposited on top of the Tuscaloosa sediments. 5) As global sea-level began to fall at the beginning of the Tertiary, Midway and Wilcox sediments were deposited over the chalk sequences (Fig. 1.23e). 6) At the end of Wilcox deposition, a relative rise in sea- level results in the onlap of basinal mudstones belonging to the Claiborne Group (Eocene) (Fig. 1.23f).

From the series of regional well-log cross-sections constructed for this dissertation, it has been possible to add further detail to this sequence of events in regards to the deposition of the Wilcox Group. First, it is apparent that at least seven deposltlonal sequences can be recognized on the Wilcox shelf-margin. These sequences are comparable to the third-order sequences of Vail et al. Figure 1.24 is a schematic representation of the spatial distribution and relative

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Figure 1.23 Generalized sequence of events leading to the development of the stable Wilcox shelf-margin. a) Initial location of lower Cretaceous shelf-margin. b) l^ajor fall in sea-level and deposition of sediments beyond the shelf-edge into deep water. c) Progradation of shallow marine elastics onto and beyond the shelf-edge. d) Continued rise in sea-level leading to the deposition of pelagic and hemipelagic muds and the extensive upper Cretaceous chalk sequences, e) As sea-level began to fall again, Midway and Wilcox elastics were deposited on top of the stable carbonate platform. f) A sea-level rise at the end of Wilcox deposition led to the deposition of pelagic and hemipelagic muds of the Claiborne Group on top of the Wilcox.

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LOWER TUSCALOOSA CRETACEOUS SHELF MARGIN TURBIDITE PHASE

DEPOSITION OF ^ DEPOSITION OF TUSCALOOSA DELTA ICS UPPER CRETACEOUS CHALKS

PROGRADATION OF ONLAP OF WILCOX CLAIBORNE

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. "OCD O Q. C g Q.

"O CD

(/) C /) TOP OF WILCOX SUPERSEQUENCE

■D8

vV-A*vVvV

CD :.v*.vv*.-v;:. •*V!«v-v!»*V!«v!»v^vVi mm:m?M\v-y mmrnm 3. :y:r:yiy:? 3" CD ■DCD O Q. liiwSPiWiWSips^*®""'''" ® C a iailiiiiifiS illiaiiiw -ii iiiin a iis^ s 3O ■D M O

CD Q. ADAMS CO. APPROX. LOCATION LIVINGSTON PH MS. BASE WILCOX OF LOWER CRETACEOUS LA

T3 REEFTREND CD

(/) C/J Figure 1.24 Stratigraphie relationships of the Wilcox supersequence within central Louisiana. Each sequence represents approximately 106 years. For most of Wilcox deposition, progradation did not bypass the Cretaceous shelf-margin. cn 52

thickness of these sequences from the stable region of the shelf-margin. It is clearly evident that a three-fold division of the Wilcox is not applicable in this region. However, it is possible that the lowermost deposltlonal sequences may not be recognizable in the updip region ('shallow Wilcox') because the regional shale markers do not extend that far updip. It is also evident from this diagram that the maximum limit of progradation did not vary significantly for most of Wilcox deposition and that the downdip limit did not extend much beyond the Tuscaloosa shelf-edge. The overall Wilcox supersequence reflects a relative balance between subsidence and deposition. In an attempt to determine if the sequences observed on the Wilcox shelf- margin formed predominately in response to cyclic fluctuations in global sea- level rather than sediment supply (Vail et al, 1977), Lowry (Chapter four) has numerically simulated the sequence boundaries and shoreline locations which would result from these sea-level curves. It was concluded from these experiments that unrealistic values for sea-level cycle wavelengths and amplitudes would be required in order to approximate the observed sequence stratigraphy of the Wilcox shelf-margin. A closer approximation of the sequences was obtained using a hypothetical eustatic sea-level curve in which there was variation in the rate of fall over a 5 x105 year period. The second major point regarding Wilcox shelf-margin deposition concerns thé role of the underlying shelf-margins. These pre-existing shelf- margins have had two important influences on the development of the Wilcox margin. First, the carbonate platform which formed behind the lower Cretaceous reef trends provided a relatively stable platform onto which successive clastic sequences could prograde. The occurrence of this stable platform meant that structural influence on the development of sequences which did not extend beyond the shelf-edge was relatively minor. Secondly, the relatively steep

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incline affronting the lower Cretaceous shelf-margin created an inherent instability (i.e. a glide plane) (Galloway, 1983) as sediments began to prograde basinward. The result of this instability was the generation of a highly unstable progradational clastic shelf-margin. There is evidence of syndepositional faulting of deep water Tuscaloosa sediments which prograded beyond the reef trend (Fig. 1.16). It appears that extensive deformation of Wilcox sediments (regional growth-faulting) was restricted to the area close to the main drainage axis of the ancestral Mississippi river. This appears to be the only region within the Louisiana Wilcox where the sequences prograded beyond the Tuscaloosa margin.

For the most part, it appears that the Wilcox shelf-margin of Louisiana may be similar to that of the modern Alabama shelf-margin (Fig. 1,25). In figure 1.25, Addy and Buffler (1984) show that the Appalachicola delta complex has not prograded beyond the Cretaceous shelf-edge. The resultant Alabama shelf- margin is predominantly stable with minimal large-scale growth-faulting. Therefore, the Alabama shelf-margin is a valuable modern example of the way

in which pre-existing topography can influence the structural and stratigraphie development of a stable progradational clastic shelf-margin.

CONCLUSIONS

1. The downdip Wilcox trend in Louisiana represents a shelf -margin setting.

2. A simple threefold division of the subsurface Wilcox in central Louisiana does not accurately describe the character of the basin-fill.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ■DCD O Q. C S Q.

■D CD N

C /) C /) G T 3 -7 2 APALACHICOLA- 10 KM DELTA FAN LOBES ?

8 MISSISSIPPI "O FAN

3 CD

3. 3" CD ■DCD O Q. C a o APALACIICOLA 3 DELTA, T3 O

(D Q.

^ LOWER O C CRETACEOUS

T3 SHELF-MARQN (D

(/) Figure 1.25 Reflection seismic profile across the Alabama shelf-margin. This C /) figure depicts the probable stratigraphie relationships of the Wilcox Group to the underlying shelf-margins in the stable region of the margin. oi 4b. 55

3. At least seven deposltlonal sequences can be recognized within the shelf- margin trend of the Wilcox in central Louisiana. These sequences are comparable to third-order global stratigraphie sequences.

4. In general, the shelf-margins which formed during Wilcox time exhibited minimal basinward displacement from their initial position.

5. The underlying carbonate platform provided a stable foundation over which successive sequences prograded. Consequently, most of the margins which formed in the central Louisiana region were relatively stable. The Alabama shelf-margin is a modern analogue for the stable shelf-margins of the Wilcox.

6. In those places where the Wilcox prograded beyond the stable platform, the margin became highly unstable and was subject to extensive syndepositional normal faulting.

7. A submarine canyon system referred to as the St. Landry Canyon occurs within the unstable region of the shelf-margin. It has a relatively shallow and broad cross-sectional profile. This feature is believed to have formed during a significant sea-level lowstand during Wilcox deposition.

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8. The potential for future hydrocarbon exploration activity along this shelf- margin trend appears quite promising. Downdip from the submarine canyon system, there is presumably a well-developed submarine fan complex with favorable exploration targets. Also, local stratigraphie traps against the canyon-fill clearly exist although their development potential is somewhat limited.

REFERENCES

Adams, G. S., 1985, Depositional history and diagenesis of the middle Glen

Rose reef complex (Lower Cretaceous), East Texas and Louisiana: Baton Rouge, Louisiana State University, Master's thesis, 200 p. Addy, 8. K. and Buffler, R. T., 1984, Seismic stratigraphy of the shelf and slope, northeastern Gulf of Mexico: Am. Assoc. Petroleum Geologists Bull., v. 68, p. 1782-1789.

Almgren, A. A., 1978, Timing of Tertiary submarine canyons and marine cycles of deposition in the southern Sacramento Valley, California, in D. J. Stanley and G. Kelling, eds.. Sedimentation in Submarine Canyons, Fans, and Trenches, Dowden, Hutchinson, & Ross, Inc., Stroudsburg, Pa, p. 276-291.

Andersen, H. V., 1960, Geology of Sabine Parish: Louisiana Geological Survey, Geological Bulletin No. 34, 164 p. Berg, O. R., 1982, Seismic detection and evaluation of delta and turbidite sequences: Their application to exploration for the subtle trap: Am. Assoc. Petroleum Geologists Bull., v. 66, p. 1271-1288.

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Berg, O. R. and Woolverton, D. G., 1984, Seismic Stratigraphy II: An Integrated Approach to Hydrocarbon Exploration, Am. Assoc. Petroleum Geologists Memoir 39, 276 p.

Bornhauser, M., 1948, Possible ancient submarine canyon in southwestern Louisiana: Am. Assoc. Petroleum Geologists Bull., v. 32, p. 2287-2290. Bouma, A. H., Stelting, C. E., and Coleman, J. M., 1984, Mississippi fan: Internal structure and depositional processes: Geo-Marine Letters, v. 3, p. 147- 153.

Bruce, 0. H., 1973, Pressured shale and related sediment deformation:

Mechanism for development of regional contemporaneous faults: Am. Assoc. Petroleum Geologists Bull., v. 57, p. 878-886. Gaughey, 0. A., 1975 a, Pleistocene depositional trends host valuable Gulf oil reserves: Oil and Gas Jour., v. 73, no. 36, p. 90-94. Gaughey, G. A., 1975 b, Pleistocene depositional trends host valuable Gulf oil reserves: Oil and Gas Jour., v. 73, no. 37, p. 240-242. Ghuber, S. and Begeman, R. L., 1982, Productive lower Wilcox stratigraphie traps from an entrenched valley in Kinkier Field, Lavaca County, Texas: Gulf Coast Assoc. Geol. Soc. Trans., v. 32, p. 255-262. Cleaves, A. W. and O’Neill, W. L., 1983, Terrigenous clastic facies distribution and lignite exploration models for the Wilcox Group of Mississippi (abs.): Abstracts with Programs Geol. Soc. America, 99 p. Giifton, H. E., 1981, Submarine canyon deposits, Point Lobos, California: in V. Frizzell, ed.. Upper Cretaceous and Paleocene Turbidites, Central California Coast, Soc. Econ. Paleontologists Mineralogists Pacific Sec., Field Trip 6, p. 79-92. Coates, E. J., 1979, The occurrence of Wilcox lignite in west-central Louisiana: Baton Rouge, Louisiana State University, Master's thesis, 249 p.

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Coates, E. J., Groat, 0. G., and Hart, G. F., 1980, Subsurface Wilcox lignite in west-central Louisiana: Gulf Coast Assoc. Geol. Soc. Trans., v. 30, p. 309-332.

Cohen, Z., 1976, Early Cretaceous buried canyon: Influenoil field, Israel: Am. Assoc. Petroleum Geologists Bull., v. 60, p. 108-114. Coleman, J. M., Prior, D. B., and Lindsay, J. P., 1983, Deltaic influences on

shelfedge instability processes: in D. J. Stanley and G. T. Moore, eds.. The Shelf break: Critical Interface on Continental l\/largins, Soc. Econ. Paleontologists Mineralogists Spec. Pub. No. 33, p. 121-137. Craft, W. E., 1966, Channel sands are the key to Wilcox oil: Oil and Gas Jour., v. 64, no. 15, p. 124-130.

Dixon, L. H., 1965, Cenozoic cyclic deposition in the subsurface of Central Louisiana: Louisiana Geological Survey, Geological Bulletin No. 42, p. 124 p.

Edwards, M. B., 1981, Upper Wilcox Rosita delta system of south Texas: Growth-faulted shelf-edge deltas: Am. Assoc. Petroleum Geologists Bull.,

V. 65, p. 54-73.

Fisher, W. L. and McGowen, J. H., 1967, Depositional systems in the Wilcox

Group of Texas and their relationship to occurrence of oil and gas: Gulf Coast Assoc. Geol. Soc. Trans., v. 17, p. 105-125. Fisk, H. N. and McFarlan, E., Jr., 1955, Late Quaternary deltaic deposits of the Mississippi River: in Crust of the Earth, Geol. Soc. America Special Paper 62, p. 279-302. Forgotson, J. M., Jr., 1957, Nature, usage and definition of marker defined vertically segregated rock units: Am. Assoc. Petroleum Geologists Bull., v. 41, p. 2108-2113.

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Frazier, D. E., 1974, Depositional-episodes: Their relationships to the Quaternary stratigraphie framework in the northwestern portion of the Gulf Coast basin: Geological Circular, 74-1, Texas Bureau Economic Geology, Univ. Texas, Austin, Texas, 28 p. Galloway, W. E., 1968, Depositional systems of the Lower Wilcox Group, North- Central Gulf Coast Basin: Gulf Coast Assoc. Geol. Soc. Trans., v. 18, p. 275-289.

Galloway, W. E. and Brown, L. P., Jr., 1973, Depositional systems and shelf- slope relations on cratonic basin margin, uppermost Pennsylvanian of North-central Texas: Am. Assoc. Petroleum Geologists Bull., v. 57, p. 1185-1218.

Granada, W. H., Jr., 1963, Cretaceous stratigraphy and structural development of the Sabine Uplift area, Texas and Louisiana: in L. A. Herrmann, ed.. Report on selected and south Arkansas oil and gas fields and regional geology, Shreveport Geol. Soc., v. 5, p. 50-96. Hardin, G. C., Jr., 1962, Notes on Cenozoic sedimentation in the Gulf Coast geosyncline, U.S.A.: in Geology of the Gulf Coast and Central Texas and Guidebook of Excursions, Houston Geol. Soc., Houston, Texas, p. 1-15. Harrison, F. W., 1980, Louisiana Tuscaloosa versus Southeast Texas Woodbine: Gulf Coast Assoc. Geol. Soc. Trans., v. 30, p. 105-109. Hendricks, L. and Wilson, W. P., 1967, Introduction: in L. Hendricks, ed., Commanchean (Lower Cretaceous) Stratigraphy and Paleontology of Texas, Basin Sec. Soc. Econ. Paleontologists Mineralogists Pub. No. 67-8, Midland, Texas, p. 1-6. Herbert, R. L., 1972, Computer mapping in the Wilcox Group (Lower Eocene), east central Louisiana: Baton Rouge, Louisiana State University, Master's thesis, 89 p.

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Howe, H. V., 1962, Subsurface geology of St. Helena, Tangipahoa, Washington, and St. Tammany Parishes, Louisiana; Gulf Coast Assoc. Geol. Soc. Trans., v. 12, p. 121-155. Hoyt, W. V., 1959, Erosionai channel in the middle Wilcox near Yoakum, Lavaca County, Texas; Gulf Coast Assoc. Geol. Soc. Trans., v. 11, p. 41-50. Hubbard, R. J., Pape, J., and Roberts, D. G., 1985 a, Depositional sequence mapping as a technique to establish tectonic and stratigraphie framework and evaluate hydrocarbon potential on a passive continental margin: in O. R. Berg and D. G. Woolverton, eds.. Seismic Stratigraphy II: An Integrated Approach to Hydrocarbon Exploration, Am. Assoc. Petroleum Geologists Memoir 39, p. 79-91. Hubbard, R. J., Pape, J., and Roberts, D. G., 1985 b, Depositional sequence mapping to illustrate the evolution of a passive continental margin; in O. R. Berg and D. G. Woolverton, eds.. Seismic Stratigraphy II: An Integrated Approach to Hydrocarbon Exploration, Am. Assoc. Petroleum Geologists Memoir 39, p. 93-115. Jackson, M. P. A. and Galloway, W. E., 1984, Structural and Depositional Styles of Gulf Coast Tertiary Continental Margins, Application to Hydrocarbon Exploration, Am. Assoc. Petroleum Geologists Note Series No. 25, Tulsa, 226 p. Lowry, P., Lemoine, R. 0., and Moslow, T. P., 1986, Sedimentary facies of the

uppermost Wilcox shelf-margin trend; South-Central Louisiana; in T. F. Moslow and E. G. Rhodes, eds.. Modern and Ancient Shelf Clastics: A Core Workshop, Soc. Econ. Paleontologists Mineralogists Core Workshop No. 9, p. 363-412.

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Mabibi, M. J., 1979, Subsurface study of the Tremont Sand, Wilcox Group, Caldwell Parish, Louisiana: Monroe, Northeast Louisiana University, Master's thesis.

Martin, R. G., 1978, Northern and Eastern Gulf of Mexico continental margin: Stratigraphie and structural framework: in A. H. Bouma, G. T. Moore, and J. M. Coleman, eds.. Framework, Facies and Oil-Trapping Characteristics of the Upper Continental Margin, Am. Assoc. Petroleum Geologists Studies in Geology no. 7, p. 21-42. Martin, R. G. and Bouma, A. H., 1978, Physiography of Gulf of Mexico: in A. H. Bouma, G. T. Moore, and J. M. Coleman, eds.. Framework, Facies and Oil-Trapping Characteristics of the Upper Continental Margin, Am. Assoc. Petroleum Geologists Studies in Geology no. 7, p. 3-19. May, J. A., Warme, J. E., and Slater, R. A., 1983, Role of submarine canyons on shelfbreak erosion and sedimentation: Modern and ancient examples' in D. J. Stanley and G. T. Moore, eds.. The Shelfbreak: Critical Interface on Continental Margins, Soc. Econ. Paleontologists and Mineralogists Spec. Pub. No. 33, p. 315-332. McFarlan, E., Jr., 1977, Lower Cretaceous sedimentary facies and sea level

changes, U. S. Gulf Coast: in D. G. Bebout and R. G. Loucks, eds., Cretaceous Carbonates of Texas & Mexico, Bureau of Economic Geology, Univ. Texas, Austin, p. 5-11. McGookey, D. P., 1975, Gulf Coast Cenozoic sediments and structure; an

excellent example of extra-continental sedimentation: Gulf Coast Assoc. Geol. Soc. Trans., v. 25, p. 104-120. Miall, A. D., 1984, Principles of Sedimentary Basin Analysis, Springer-Verlag, New York, 490 p.

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Mulcahy, S. A., 1981, Near-surface lignite occurrence, Sabine Uplift, northwest Louisiana: Baton Rouge, Louisiana State University, Master's thesis, 190

p. Murray, G. E., 1948, Geology of DeSoto and Red : Louisiana Geological Survey, Geological Bulletin No. 25, p. 312 p. Murray, G. E. and Thomas, E. P., 1945, Midway-Wilcox surface stratigraphy of the Sabine Uplift, Louisiana and Texas: Am. Assoc. Petroleum Geologists Bull., v. 29, p. 45-70. Picha, F., 1979, Ancient submarine canyons of Tethyan continental margins, Czechoslovakia: Am. Assoc. Petroleum Geologists Bull., v. 63, p. 67-86. Pitman, W. 0., 1978, Reiationship between eustacy and stratigraphie sequences of passive margins: Geol. Soc. America Bull., v. 89, p. 1389- 1403. Purcell, M. D., Hart, G. P., and Groat, 0. G., 1985, Subsurface lignite occurrence in Wilcox Group, Northeast Louisiana and Northwest Mississippi: Gulf Coast Assoc. Geol. Soc. Trans., v. 69, p. 1429. Rogers, J. D., 1983, The occurrence of deep basin lignite in the Wilcox Group of northeast Louisiana: Baton Rouge, Louisiana State University, Master's thesis, 165 p.

Shepard, F. P., 1981, Submarine canyons: Multiple causes and long-term persistence; Am. Assoc. Petroleum Geologists Bull., v. 65, p. 1062-1077. Sloss, L. L., 1963, Sequences in the cratonic interior of North America: Geol. Soc. America Bull., v. 74, p. 93-114. Sloss, L. L., 1984, Comparative anatomy of cratonic unconformities: /n J. S. Schlee, ed.. Interregional Unconformities and Hydrocarbon Accumulation, Am. Assoc. Petroleum Geologists Memoir 36, p. 1-6.

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Smith, G. W., 1981, Deposltiotjal environments of the 20,300 foot and 19,000 foot sandstones at Judge Digby and False River Fields, Pointe Coupee and West Baton Rouge Parishes, Louisiana: in Recognition of Shaliow- water versus Deep-water sedimentary facies in growth-structure affected formations of the Guif Coast Basin, Gulf Coast Section Soc. Econ. Paleontologists. Mineralogists, 2nd. Annual Research Conf., Dallas, Texas, p. 62-67.

Smith, G. W., 1985, Geology of the deep Tuscaloosa (upper Cretaceous) gas trend in Louisiana: in B. F. Perkins and G. B. Martin, eds.. Habitat of Oil and Gas in the Gulf Coast, Gulf Coast Section Soc. Econ. Paleontologists Mineralogists, 4th Annual Research Conf., Houston, Texas, p. 153-190. Smithwick, J. A., 1954, Subsurface correlation of the Wilcox Group in Louisiana: Baton Rouge, Louisiana State University, Master's thesis, 63 p. Steffens, G. S., 1986, Pleistocene entrenched valley/canyon systems. Gulf of Mexico (abs.): Am. Assoc. Petroleum Geologists Bull, v. 70, p. 1189. Swift, D. J. P., 1968, Coastal erosion and transgressive stratigraphy: Jour. Geol,

V. 76, p. 444-456. Vail, P. R., Mitchum, R. M., and Thompson, S., ill, 1977, Seismic stratigraphy and global changes in sea level. Part 3: Relative changes of sea level from coastal onlap: in C. E. Payton, ed.. Seismic Stratigraphy - Applications to Hydrocarbon Exploration, Am. Assoc. Petroleum Geologists Memoir 26, p. 63-97.

Vormelker, R. S., 1980, Texas Middle Wilcox channel: Oil and Gas Jour., v. 78, p. 136-154.

Winker, C. D., 1982, Cenozoic shelf margins, northwestern Gulf of Mexico: Gulf Coast Assoc. Geol Soc. Trans., v. 32, p. 427-448.

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Winker, C. D., 1984, Clastic shelf margins of the post-Commanchean Gulf of Mexico: Implications for deep-water sedimentation: Gulf Coast Section Soc. Econ. Paleontologists Mineralogists Foundation Research Conference, Austin, Texas, p. 282-293. Winker, C. D. and Edwards, M. B., 1983, Unstable progradational clastic shelf margins: in D. J. Stanley and G. T. Moore, eds.. The Shelfbreak-Critical interface on Continental Margins, Soc. Econ. Paleontologists Mineraiogists Spec. Pub. No. 33, p. 139-157. Woodbury, H. O., Murray, I. B., Pickford, P. J., and Akers, W. H., 1973, Pliocene and Pleistocene depocenters, outer continental shelf of Louisiana and Texas: Am. Assoc. Petroleum Geologists Bull., v. 57, p. 2428-2439.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER II

SEDIMENTARY FACIES OF THE UPPERMOST WILCOX SHELF-MARGIN TREND: SOUTH-CENTRAL LOUISIANA

ABSTRACT

Fordoche field, which has estimated reserves in excess of 90 million barrels of oil and gas, contains several stacked sandstones that are part of a paleo shelf-margin trend within the downdip uppermost Wilcox of south-central Louisiana. Commonly referred to as the 'Deep Wilcox,' this trend contains at least one submarine canyon-fill and is coincident with the underlying Cretaceous carbonate reef trend. Thus, antecedent topography has significantly influenced the patterns of sedimentation and preserved sand-body geometry within this downdip Wilcox trend.

The main reservoir intervals appear 'blocky' on electric logs and their average thickness is 9.14 to 12.2 m (30 to 40 ft). They are laterally continuous in an east-west (strike) direction over a distance of 64.5 km (40 mi) and in a north- south (dip) direction over a distance of at least 9.68 km (6 mi). Analysis of over 91.4 m (300 ft) of conventional core from the W8 sandstone within Fordoche field suggests deposition in a wave-dominated shoreface environment at or near the shelf-margin. Use of the term 'shelf-margin delta' or 'shelf-edge delta' has been avoided only because there is no direct evidence in the cores of a developed fluvial system; however, the sandstone bodies are believed to be somewhat analogous to late Quaternary Gulf Coast shelf-margin deltas.

65

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Six major lithofacies ('A' through 'F') are identified within the W8 sandstone. Facies A through C, which constitute over 90% of the cored sequence, represent the initial progradation of inner-shelf and shoreface sandstones over outer-shelf and upper-siope mudstones. Facies D and E are sandstones and sandy mudstones that represent the remnants of a transgressive event that reworked upper shoreface and foreshore deposits. Facies F is composed of mudstones that represent suspension sedimentation in an outer-shelf environment associated with the ongoing transgression. Optimum reservoir quality is associated with the less bioturbated upper portion of facies C. However, the highest permeability and porosity values occur within thin, discrete sandstone beds (5 to 30 cm: 1.95 to 11.7 in thick) (interpreted as tempestites) in facies B which underlies the main reservoir sandstone. These beds have been interpreted as tempestites, several of which produce hydrocarbons. Hov/ever, many of these beds are frequently bioturbated, thereby impairing reservoir homogeneity.

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INTRODUCTION

Wilcox in Louisiana

The Wilcox Group (Paleocene-Eocene) (Fig. 2.1) is a well-established and prolific hydrocarbon sequence in the northern Gulf of Mexico basin. Locally, the Wilcox is over 1,219 m (4,000 ft) thick and represents the initial influx of terrigenous clastic sediments to the Louisiana region of the basin during the early Tertiary. The majority of Wilcox oil and gas production within Louisiana originates from relatively shallow (914 to1,828 m; 3,000 to 6,000 ft), dip-oriented sandstone reservoirs in the northern region of the state (Craft, 1966). Toward the south and downdip from this developed region is a strike-oriented trend which extends 225.8 km (140 mi) from Livingston Parish in the east to the Texas-Louisiana state line in the West (Fig. 2.2). The average depth of the producing intervals is 3,048 to 4,267 m (10,000 to 14,000 ft). Significant oil and gas fields within the downdip 'Deep Wilcox' trend include Fordoche field (Point Coupee Parish) and Lockhart Crossing and Livingston fields (Self et al, 1985).

The purpose of this study is to examine the nature, distribution, and reservoir quality of sedimentary facies from a producing interval within this downdip trend in south-central Louisiana. This examination is based on the sedimentologic analysis of conventional cores from Fordoche field. In addition to core analysis, well-log correlations are used to construct cross sections that provide a regional stratigraphie perspective of the producing interval.

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ERA SYSTEM SERIES ROCK UNIT

QUATERNARY PLEIS1

CITRONELLE FM.

FLEMING FM.

CATAHOULA FM.

VICKSBURG GRP.

JACKSON GRP.

CLAIBORNE GRP.

WILCOX GRP.

MIDWAY GRP.

Figure 2.1 Generalized Guif Coast Cenozoic stratigraphie column.

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C/) C/)

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BASM RESEARCH MSTITUTE LOUISIANA STATE UWERSITY ■D CD Figure 2.2 Location map of oil and gas fields in central Louisiana showing structural contours on top of the Wilcox. The enclosed region in the (/) lower part of the map is the study area for this investigation and shows the location of regional strike and dip cross sections in Figures 2.5 and 2.6 (modified from Oil and Gas Map of Louisiana. Louisiana Geological Survey, 1981). O) (O 70

Stratigraphie Nomenclature

Owing to a limited number of surface exposures and pervasive lateral facies changes, correlation of formations from surface to subsurface has met with minimal success in Louisiana. Consequently, many subsurface geologists have adopted a simplistic threefold division of the Wilcox section based on electric-log pattern recognition (AIbach, 1979; Coates, 1979; Mulcahy, 1981; Rogers, 1983). The lower, middle, and upper Wilcox are interpreted as fluvial- dominated deltaic; deep-marine; and wave-dominated deltaic systems, respectively (Fisher and McGowen, 1967; Galloway, 1968). In practice, recognition of this threefold division within the Wiicox of Louisiana may obscure true stratigraphie relationships. In this paper, reference is made to locations within the section as being lowermost or uppermost simply to indicate relative position in the section and thus avoid possible unwarranted genetic connotations.

The most basinward trend of Wilcox production is frequently termed the 'Deep Wilcox' because of the subsea depth of production intervals (Berg and Tedford, 1977; Edwards, 1980). Since most hydrocarbon production from this trend originates from the uppermost Wilcox sandstones, preference is given here to the term 'downdip uppermost Wilcox' to avoid confusion regarding the relative depth of reservoirs within the section.

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BfiflioiiaLQeQioqiç Setting

The Wilcox Group is the lowermost portion of a thick sequence of Tertiary clastic sediments deposited along the northern rim of the Gulf of Mexico basin. A narrow band of Wilcox outcrops extends from Alabama to Texas, but for the most part, the majority of the section is confined to the subsurface. Consequently, much of the present understanding of Wilcox depositional history is based primarily on well-log correlations and subsurface facies analysis (Fisher and McGowen, 1967; Galloway, 1968). Three important aspects of the regional geologic setting of the present study area help improve our understanding of the paleogeography and stratigraphy of the uppermost Wilcox. First, through the analysis of foraminiferal assemblages, Anisgard (1970) determined that most of the mudstones of the downdip Wilcox trend were deposited in inner to middle-neritic marine conditions where average water depths were 30.5 m (100 ft). The foraminiferal assemblages were interpreted to be characteristic of turbid, poorly-oxygenated marine waters.

Secondly, Winker and Edwards (1983) documented the effect of a previously established Cretaceous shelf-margin on all subsequent deposition. From early Cretaceous to the Paleocene, shelf-margins remained within a relatively confined zone (Fig. 2.3) (Hendricks and Wilson, 1967; Stehli et al, 1972; Christina and Martin, 1979; Winker, 1982). The early Cretaceous carbonate shelf-edge reef trend formed a stable, well-defined margin. When this margin was eventually overlain by clastic sediments, the flexure controlled the location of successive shelf-edges and created a regional zone of instability.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CD ■ D O Q. C g Q.

"D CD

C/) C/) LOWER CRETACEOUS SHELF MARGIN TUSCALQOSA/WOODBINE SHELF MARGIN ■D8 WILCOX SHELF MARGIN

CD ST. LANDRY YOAKUM CANYON 3. 3" CHANNEL CD ■DCD O Q. C a <— 3O "O o

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■D CD Figure 2.3 Map of lower Cretaceous, Tuscaloosa/Woodbine, and Wilcox shelf- margin trends in the northern Gulf Coast with locations of Yoakum C/) C/) Channel and St. Landry Canyon (modified from Winker, 1982).

N tV) 73

The third aspect of the regional geologic setting pertinent to this study area is the discovery of a large mudstone-filled channel in St.Landry Parish (Fig. 2.3) (Lowry et al, 1986; McCulloh and Eversull, 1986). This feature is interpreted to represent a Wilcox submarine canyon system and appears similar to other thick mudstone channel-fiils in Texas (Hoyt, 1953; Chuber and Begeman, 1982). Given that modern submarine canyons (e.g. Mississippi Canyon) form at or near the shelf-margin, data from this study, when merged with previous paleontological and stratigraphie findings, suggest that sediments of the downdip Wilcox trend in Louisiana were deposited close to the shelf-margin.

FORDOCHE FIELD

Development History

Wilcox production in Fordoche field was first established in November 1965 from the Sun Kent #1 discovery well (Pierson, 1970). The Kent #1 well is significant in that it helped establish a new production trend in the downdip Wilcox in south-central Louisiana. Initial production was 411 barrels per day from two intervals. The shallowest interval occurs at 4,201 to 4,205 m (13,784 to 13,796 ft) and the deeper interval at 4,247 to 4,262 m (13,933 to 13,983 ft). Fordoche field occurs within a 'deep-seated' anticline associated with a major growth-fault. There are five producing intervals within the field, referred to as the W4, W5, W8, W12, and W15 sandstones (Fig. 2.4). This paper examines the sedimentary characteristics and reservoir quality of the W8 sandstone. Estimated reserves-in-place for Fordoche field are approximately 91

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N. SMITH JR. #8 SEC. 41, T6S R8E

RES mV ohms-mVm SFl

TOP WILCOX

W4

W5

we

W I2

W15

Figure 2.4 Wilcox "type-log" for Fordoche Field from the N. Smith Jr. #8 well. Core sequences from the W8 Sandstone (stippled) are examined in this study. Main producing intervals are labeled (Modified from Eckles et al., 1981).

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million barrels (91 mm bbl.). However, as of 1983, ultimate recovery after reservoir stimulation was estimated at only 27.6 million barrels (27.6 mm bbl.) or 30%. Sun Oil Company, the major operator in the field, began a miscible gas enhanced-recovery project that has proved to be very successful. Nitrogen injection from three wells greatly increased reservoir pressures and flow rates, especially for the W8 sandstone. The W8 interval has yielded 11.7 million barrels (11.7 mm bbl.) of highly volatile oil (45.8° API gravity), which is approximately 31% of the estimated oil in place. Information gained from this study pertaining to the input of depositional controls on reservoir quality and performance should be helpful in planning any further enhanced-recovery projects.

Reservoir geometrv and growth-faulting

The W8 sandstone is one of three thick sandstone intervals that occur within a sedimentary package which is 64.5 km (40 mi) long and almost 91.4 m (300 ft) thick (Fig. 2.5). All three sandstones rapidly pinch out over 9.68 to 11.29 km (6 to 7 mi) in a basinward direction (Fig. 2.6). Updip, the character of the package, as determined from well-logs, is significantly different and consists of interbedded sandstones and shales (Fig. 2.6).

It is clearly evident from figure2.6 that faulting has had a significant influence on deposition in this area. It has been interpreted that fault A (Fig. 2.6) was active during Wilcox deposition, whereas movement on fault B occurred after Wilcox deposition. Both of the faults depicted on the dip cross-section are major syndepositional faults, commonly referred to as growth-faults (Lehner, 1969; Busch, 1975). Growth-faults are very common at unstable shelf-margins

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(/) STRIKE CROSS SECTION (/) (W) (E) 3o '

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"D CD (N) DIP CROSS SECTION (S) BARlON # I SHHRBURNB LAND #1 JUMONVILLB #1 PARDEH #I-A C/) S K M. N S R7I. SI C 24. I « i R7h SI C 4 ». r w R7I. S H 7. T?S R7I: C/) V IfS lO f WMCOI

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■O CD Figure 2.6 Regional dip-oriented crcss-section (B-B') through the uppermost Wilcox of the study area (see Fig. 2.2 for location of section). The W8 C/) C/) Sandstone is stippled in the Sherburne Land #1 well which was used to define the along-strike continuity of the W8 in cross section A-A' (Fig. 2.5). Note rapid lateral facies changes in the W8 in a downdip and updip direction. •Nl 78

(Jackson and Galloway, 1984; Winker and Edwards, 1983). The net result of this type of faulting is a thickening of section on the downthrown side of the fault and the development of rollover anticlines (Durham and Peoples, 1956; Martin, 1978). Such rollover anticlines are perhaps the most common exploration prospect in the Gulf Coast. Although the influence of growth-faulting can be demonstrated on a large vertical scale (3.28x10^ to 3.28x10^ m: 10^ to 10^ ft) (Thorsen, 1963), its effect on a discrete depositional event (e.g. a progradational shoreface sequence which may be 10 to 15 m (32.81 to 49.2 ft) thick is less clear. Edwards (1981) suggests that growth-faulting played an important role in the development of upper Wilcox shelf-edge deltas in southern Texas, whereas Suter and Berryhill (1985) concluded that it had relatively little influence on the development of Gulf Coast late Quaternary shelf-margin deltas. The results of this study indicate that, although growth-faults are apparently important, they may not be a necessary precursor to the development of strike-oriented sandstone bodies at the shelf- edge.

CORED SEDIMENTARY FACIES

Vertical Sequence

Approximately 91 m (300 ft) of conventional cores from five different wells were used to examine the W8 sandstone of Fordoche field (Fig. 2.7). A detailed sedimentoiogic description was written for all cores in order to determine the following: (1) the sedimentary characteristics and recognition criteria of distinct lithofacies, (2) the processes responsible for deposition of the sediments, (3) the

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Huditone (SOI clay. Muddy, very-fine Silty, very-fine Very-fine grained, Very fine sandy M udstone (40% c l a y , sllt) thln(l-lOm) grained sandstone grained, well sorted calcareous sandstone mudstone (60% sand); 55% s i l t ) ; g la u ­ sllt lenses dispersed (» e a n 9f)-lOO**, sandstone (mean 100- (mean 1 0 0 -1 2 3 » , max glauconite 10-15%. conite 1-3%: thrnughouc Interval, ■ax 125^), with 123#, max 130#); 130m); diverse small slderite concretions. localised con­ g la u c o n ite <1Z; thln(5-30ca)sllty. glauconite «2Z. (3-lOsem) carbonate centrations of localized concen­ very-fine grained p y r i t e «2%. trations of pyrite sandstone interbeds; * 2 Z . glauconite 2-31; pyrite ^IZ.

PHYSICAL Lenticular bedding Horiaontal to sub- Massive appearing Massive appearing. Rare horizontal Horizontal laminations. SEDIMEmRV soft sediment de­ horizontal lamina­ (b u rro w e d ? ); laminations. STRUCTURES formation; rare tions; rare low rare horizontal load-casted ripples. angle truncation laminations.

6I0CE.NIC Rare burrowing; low Common b u rro w in g : Abundant burrowing; No d i s t i n c t burrow S io tu r b a ta d (>73% Rare burrowing; SEOtHENTARY diversity of burrow moderate diversity low diversity of b u rro w e d ). low diviirsity of STRUCTURES ty p e 8 ( C h o n d r ite s , of burrow types burrow types burrow types Terebellina). (Teiichichnus, (Opbiomorpha). (Terebellins), Terebellina, Planolltes, Chondrites).

SEQUENCE Lower contact missing, Sandstone beds Lower contact grada­ Lower and upper Lower contact sharp, Lover contact grada­ CHARACTERISTICS gradational upper exhibit sharp tional, sharp upper contacts sharp. gradational upper tional, upper contact c o n t a c t ; d e e r a a te in lower contacts contact; increase In contact; decrease in sharp; increase in silt soft-sediment de­ and burrowed upper sand Content and glauconite and content upwards. formation and increase contacts; Increase decrease in degree of i n c r e a s e in mud in burrowing upwards. in thickness and burrowing upwards. contents upwards. frequency of occurrence of discrete sandstone beds upwards.

RESERVOIR Not a reservoir unit. Discrete sandstone 0 ...... 15-22% 0 ...... 4% 0 ...... 6-12% Hot a reservoir unit. (QUALITY • beds K...... 0.5-l«ad K ...... O .lm d K .. . . O.lm d 0 ...... 10-231 S ...... 20-30% S ...... 7% S •• ...0 -4 % K ...... IO-98md (best reservoir ( p o s s ib le >5-2» quality facies) diagenetic seal) Koddy sandstone beds 0 ...... 10-15% K ...... 0 .i-3 m d So.... ” *fiased on Porosity (0 ), Permeability (K), and Oil Saturation (S.).

Table 2.1 Sedimentary characteristics and relative reservoir quality of cored facies.

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environment in which the sediments were deposited, and (4) the relationship between primary patterns of sedimentation and reservoir quality. Six distinct sedimentary facies (A to F) have been recognized in the W8 sandstone interval. On the basis of core analysis, a summary of sedimentary characteristics (i.e. lithology and physical and biogenic sedimentary structures), sequence characteristics, and relative reservoir quality for all facies has been compiled (Table 2.1). A composite sedimentary sequence showing the vertical succession of facies in the W8 sandstone has been compiled principally from analysis of core from the N. Smith Jr. #8 well located near the central portion of Fordoche field (Figs. 2.7, 2.8).

The vertical sequence of facies in the W8 interval is dominated by a relatively thick (10.67 to 12.19 m: 35 to 40 ft), burrowed, and massive-appearing sandstone (facies C) that shows an upward increase in sand percentage. Underlying and gradational with facies C is a burrowed muddy sandstone with laminated sandstone interbeds (facies B). Facies B and C are the major reservoir units in the W8 interval. In almost all producing wells, facies C is capped by a thin (0.61 to 0.91 m: 2 to 3 ft), calcareous, tightly cemented, very fine-grained sandstone that appears to be a potentially important diagenetic reservoir seal. Contorted and lenticular-bedded mudstones of facies A underlie the interbedded sandstone interval (facies B). Bioturbated sandy mudstones (facies E) and lenticular-bedded to laminated mudstones (facies F) overlie the main sandstone interval (Fig. 2.8).

A complete succession of photographs showing sedimentary structures and lithologies for the entire cored interval from the N. Smith Jr. #8 well is provided in figures 2.9 to 2.17. The descriptions of the individual facies presented below are arranged from shallowest to deepest in order to facilitate

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WC/) FORDOCHE FIELD o" 3 POINTE COUPEE PARISH, LA 0 116 117 5 20 CD 24 101 8

ci' 25 27 28 29 3026 3" 107 119

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1": 8000' % GAS W tll 4kilom eters Cofto S«» . ISU ■D CD I WC/) Figure 2.7 Map of Fordoche Field. Note locations of cored wells including the o" N. Smith Jr. #8 well in T6S, RBE, sec. 41. Cross-section C-C is through the central axis of the field.

00 32

N. SMITH JR. #8 '/ / . / / / / /

FORDOCHE FIELD FACIES "F" POINTE COUPEE PH., LA Unt

FACIES “ Ê"

FACIES "D" % A Cokoreow v try fine sond

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Figure 2.8 Schematic core description for N. Smith Jr. #8 well. This sequence IS interpreted to be characteristic of the W8 Sandstone.

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sequential reference to the core photographs. Facies A through F and the contacts between these facies are labeled in the photographs in order to facilitate correlation with the core description shown in figure2.8.

Facies F

Facies F (Cored interval: 13,172 to 13,178 ft) is a lenticular-bedded and laminated mudstone (55% silt and 40% clay). A gradual decrease in the presence of glauconite from less than 3% at the base to less than 1% at the tojD of the unit is observed. Traces of pyrite (< 2%) are concentrated adjacent to and within silt-filled burrows. Siltstone laminae are 3 to 5 mm (0.12 to 0.2 in) thick on an average and contain both connected and disconnected lenses (Fig. 2.9). Burrow types within the interval are primarily horizontal, silt-filled and ovate. Overall diversity and abundance of burrow types is low.

Facies E

Facies E (Cored interval; 13,178 to 13,181.5 ft) is a glauconite-rich (10% to 15%), bioturbated sandy mudstone. The diameter of individual glauconite pellets ranges in size from 3 to 6 mm (0.12 to 0.23 in). The sand fraction (mean grain size, 80 to 90 pm) constitutes 40% of the total interval and decreases in abundance upward to less than 10%. This unit is extensively burrowed to bioturbated (Figs. 2.9, 2.10). Rare horizontal laminations are the only physical sedimentary structures that have been observed. Slderite concretions are also present in this facies. The uppermost contact is gradational over a 30 to 40 cm (11.7 to 15.6 in) interval and corresponds to a gradual decrease in glauconite content. The lower contact is sharp.

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3 1 7 2 AC E

FACIE . p .

Figure 2.9 Core photograph of 13, 172-13, 181 ft (4,015-4,018 m) from the N. Smith Jr. #8 well showing the lowermost portions of facies F and uppermost portions of facies E. Lenticular bedding (a), glauconite pellets (b), and slderite concretions (c) are shown. Core is approximately 3 in. (7.5 cm ) in diameter.

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13 18 1

Figure 2.10 Core photograph of 13,181-13, 192 ft (4,018-4,021 m) from the N. Smith Jr. #8 well. Note sharp contact (arrow) between facies 0 and facies D. Carbonate concretions (d) are common features in facies D.

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20 0 . j I

Figure 2.11 Core photograph of 13,192-13,203 ft (4,021-4,024 m) from the N. Smith Jr. #8 well showing the massive-appearing sandstones characteristic of facies 0.

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1 3 2 0 3

Figure 2.12 Core photograph of facies 0 from 13,203-13,213 ft (4,024-4,027 m) In the N. Smith Jr. #8 well. Note decrease In the amount of burrowing upward.

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1 n o 1 ^

Figure 2.13 Core photograph of 13,213-13,223 ft (4,027-4,030 m) from the N. Smith Jr. #8 well. Note location of Ophiomorpha burrow at 13,214.5 ft (see Fig. 2.19A).

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1 3 2 2 3

i

ACIES

Figure 2.14 Core photograph of 13,223-13,233 ft (4,030-4,033 m) from the N. Smith Jr. #8 well showing characteristic features of facies B. Note amalgamation of sandstone beds (e) at 13,224 ft and discrete sandstone beds at 13,224.5 ft (see close-up photo in Fig. 2.20A).

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1 3 2 3 3

. ,.v'%

I

' i

Figure 2.15 Core photograph of facies B from 13,233-13,243 ft (4,033-4,036 m) in the N. Smith Jr. #8 well. Note Planolites burrow (f), and Teichichnus burrow (g). Thin discrete sandstone bed at 13,237.2 ft is shown in close-up photo in Figure 2.200.

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1 3 2 4 3

• y Figure 2.16 Core photograph of 13,243-13,250 ft (4,036-4,039 m) from the N. Smith Jr. #8 well. Note Terebellina burrow (h) and Chondrites burrow (i) in facies B. Load-casted ripple at 13,245.8 ft is shown in detail in Figure 2.21 A.

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1 3 2 5 0

Figure 2.17 Core photograph of facies A from 13,250-13,260 ft (4,039-4,042 m) in the N. Smith Jr. #8 well. Note contorted (j) and lenticular (k) bedding. Contorted bedding at 13,251.6 ft is shown in detail in Figure 2.21 C.

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Facies D

Facies D (Cored interval: 13,281.5 to 13,283 ft) is a calcareous, very fine­ grained sandstone. It is a massive-appearing, relatively thin unit (0.5 m: 1.64 ft) and exhibits g rain-size characteristics similar to those of facies 0 (mean grain size, 100 to 125 pm; maximum, 150 pm). However, facies 0 and D differ mineralogically by the presence of abundant, diverse calcareous fragments and epigenetic carbonate concretions in facies D (Fig. 2.10). Individual foraminifers {Miliolid) and bivalve and gastropod fragments are present within this facies (Fig. 2.18). The localized abundance of carbonate material has yielded a tightly cemented interval overlying the main reservoir sandstone. No physical or biogenic sedimentary structures are observed in facies D.

Facies C

Facies 0 (Cored interval: 13,183 to 13,223 ft) Is a burrowed and massive- appearing, very fine-grained sandstone. It represents the major producing reservoir within the W8 sandstone. The average thickness of facies C within the central part of the field is 12.2 m (40 ft). Relative proportions of sand-size and silt-size material range from 60% to 30%, respectively, near the base, and from 80% to 15%, respectively, throughout the remainder of the interval. Average grain size is 100 to 125 pm with a maximum of 150 pm. Traces of glauconite (< 2%) are also present. There is a general 'cleaning-upward' trend within the facies as the mud content decreases in an upward direction. The entire interval has been extensively burrowed and, therefore, few physical sedimentary structures are preserved (Figs. 2.10, 2.11, 2.12, 2.13). Ophiomorpha burrows are the predominant burrow type and are most common

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Figure 2.18 Close-up photograph of calcareous sandstone from facies D (see Fig. 2.10 at 13,182 ft). Note abundant shell fragments.

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in the lower half of the facies (Figs. 2.19a, b). In the upper half of the unit, fewer distinct burrows can be recognized and the intensity of burrowing decreases.

Facies B

Facies B (Cored interval; 13,223 to 13,245 ft) is a burrowed muddy sandstone with laminated sandstone interbeds. It is an interbedded unit which grades from a sandy mudstone at the base (20% sand) to a muddy, very fine­ grained sandstone (70% to 80% sand) at the upper contact. Well-sorted, very fine-grained sandstone (mean grain size, 90 to 100 pm) beds, ranging from 5 to 30 cm (1.95 to 11.7 in) thick, are interbedded with the burrowed muddy sandstone (Figs. 2.14, 2.15, 2.16). Glauconite (2% to 3%) occurs throughout, with traces (< 1%) of pyrite occurring primarily in the basal portions of the unit. The discrete sandstone beds within facies B exhibit sharp lower contacts (Figs. 2.14, 2.15, 2.20a, c). Individual bed thickness in addition to the frequency of occurrence of individual beds increases upward in the sequence (Fig. 2.14). The thickest of the sandstone beds (30 cm: 11.7 in) occurs near the top of facies B and may represent amalgamation of smaller individual beds. Although many of the sandstone beds are massive in appearance (Fig. 2.20a, c). X-ray radiographs reveal horizontal to low-angle planar-tabular laminations near the base of each bed (Fig. 2.20b). Fine-scale, normal-graded bedding is also observed in the discrete sandstone beds of facies B (Fig. 2.20d).

Numerous burrows occur within facies B, including Teichichnus, Planolites, and Terebellina (Figs. 2.15, 2.16). The diversity of burrows is generally low to moderate. The greatest diversity occurs within the muddy sandstone. It should also be noted that the discrete sandstone beds of facies B

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Figure 2.19 [A] Close-up photograph of burrowed sandstone from facies C (see Fig. 2.13 at 13,214.5 ft). Note abundance of Ophiomorpha burrows (1). [B] X-ray radiograph of cored interval in Figure 2.19A. Note abundance of burrowing and lack of any preserved physical sedimentary structures.

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S g K Bswww »

Figure 2.20 [A] Close-up photograph of thin (<5 cm) very fine-grained sandstone bed in facies B (see Fig. 2.14 at 13,224.5 ft). [B] X-ray radiograph of cored interval in Figure 2.20A. Note faint horizontal to low-angle planar-tabular laminations at the base of the photo (m). [G] Close-up photograph of thin (<5 cm) very fine-grained sandstone bed from facies B (see Fig. 2.15 at 13,237.2 ft). Note sharp lower contact (n) and burrowed upper contact (o). [D] X-ray radiograph of cored interval in Figure 2.20C. Note horizontal laminations and normal grading within laminations. Arrows represent coarser- grained (light) and finer-grained (dark) sediment. Also, note burrowing which has subsequently destroyed laminations.(p).

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have the highest recorded permeability and porosity values (98 md and 25%, respectively), as determined from plug data (Table 2.1).

Facies A Facies A (Cored interval: 13,245 to 13,260 ft) is a mudstone (50% clay; 45% silt) which is characterized by the presence of contorted and lenticular beds (Figs. 2.16, 2.17). Lenticular siltstone beds are 1 to 10 mm (0.039 to 0.39 in) thick, flat, and connected. Traces of glauconite (< 1%) occur adjacent to fragments of organic detritus, primarily in the lower portion of the interval. Contorted bedding in facies A is a product of soft-sediment deformation which exhibits components of thrusting and considerable disruption of the original bedding (Figs. 2.17, 2.21c). Approximately 40% of facies A exhibits this style of bedding. The most abundant physical sedimentary structures are thin (1 to 3 mm: 0.039 to 0.12 in), streaky, and lenticular siltstone laminations. In a few places, these siltstone lenses may be recognized as load-casted ripples (Figs. 2.16, 2.21a, b). These sedimentary structures indicate a depositional environment in which the hydraulic regime was constantly fluctuating between periods of increased and decreased fluid motion, and/or sediment supply was episodic.

Biogenic activity, as recognized by the degree of burrowing in the facies, is relatively low (< 10% of the cored interval). Few distinct burrows can be recognized; however, those which do occur are primarily ovate, less than 1.5 cm (0.585 in) in diameter, horizontal, and siltstone filled.

Distinction of the upper contact between facies A and B (Fig. 2.16) is based on the following parameters: 1) a decrease in the amount of soft-sediment deformation, and 2) an increase in the degree of siltstone laminations.

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■ O CD

(/) ICI 13251.6

IB]

Figure 2.21 [A] Close-up photograph of a load-casted ripple from fades A (see Fig. 2.16 at 13,245.8 ft). [B] Sketch of cored interval in Figure 2.21 A. Note truncation surfaces of individual laminations. [0] Close-up photograph of cored interval in facies A ilustrating contorted bedding resulting from soft-sediment deformation (see Fig.2.17 at 13,251.6 ft).

to (D 100

DEPOSITIONAL PROCESSES AND EVENTS

Evidence from physical and biogenic sedimentary structures observed in the cored interval suggest three major events: (1) initial deposition during progradation of inner-shelf and shoreface sediments over outer-sheif/upper- slope muds (facies A to 0); (2) erosion of upper shoreface and foreshore sediments during a subsequent transgression and development of a ravinement surface (facies D); and (3) continued sea-level rise and deposition of shelf muds below storm wave-base (facies E and F). Data suggest that facies A was deposited in an outer shelf to upper slope setting. While dominated by deposition from suspension of muds, this environment was punctuated by periods of increased energy and sediment (i.e. siit and sand) availability. The occurrence of discontinuous siltstone lenses reflects the development of small-scale ripple-bedding in an otherwise sediment-deficient environment. The frequent occurrence of contorted bedding in facies A appears to be a product of deposition on an unstable substratum which was subject to gravity-flow processes. Another important aspect of this facies is the lack of biogenic sedimentary structures. This suggests that either sedimentation rates were extremely high or that the environment was hostile to benthic organisms. Since the mudstones in the overlying facies (B) are extensively burrowed, it has been concluded that facies A was deposited under oxygen-deficient conditions (Anisgard, 1970). The common occurrence of pyrite nodules in facies A also suggests that deposition occurred under reducing conditions. Increasing biogenic activity in the overlying facies occurs in response to the development of more oxygenated marine conditions.

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In addition to the increase in abundance and diversity of burrow types in facies B, there is a concomitant increase in the frequency and intensity of episodes of coarser-grained (i.e. fine sand size) sedimentation. Sedimentary structures and sequences within the discrete sandstone beds are similar to those observed by Brenchley (1985). The sharp basal contact in each bed is believed to form in response to initial erosion by basinward-directed geostrophic flows (Swift et al., 1985). The upper contact became burrowed during postdepositional fair-weather periods. With the exception of horizontal parallel laminations and minor normal-graded bedding, none of the beds examined contained the idealized tempestite sequences described by Bourgeois (1980), Aigner (1985), or Walker (1984). It is possible that extensive burrowing at the upper contact destroyed any manifestation of hummocky or wave-ripple cross-stratification. However, it is worth noting that the dimensions of hummocks (1 to 3 m; 3.28 to 9.84 ft) are such that direct observation of this stratification type in cores with a diameter of 6 cm (2.34 in) is extremely difficult. Therefore, indirect evidence such as low-angle truncation surfaces; multiple directions of dip of laminasets; draping of laminae; and erosional lower contacts can be used to Infer the presence of this feature in conventional cores. On the basis of characteristics including trace fossil assemblage; high abundance and diversity of burrow types; and the increasing frequency and upward thickening of sandstone beds, this facies is interpreted to have formed in a zone seaward of fair-weather wave-base, but within storm wave-base.

Facies C reflects deposition in an environment dominated by biogenic activity. There is, however, a subtle yet significant change in the relative rate of physical versus biogenic processes within the facies. In the lowermost half of

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dispersed throughout the sandstone matrix. Although grain size remains essentially unchanged, the degree of burrowing and mud content decreases, thereby reflecting an increasing influence of physical processes (waves). Within the upper part of facies C, localized horizontal planar-tabular laminations are found. These parallel laminations probably formed as a result of deposition from suspension. Sediment was suspended in response to increased wave activity which suggests an aggradation of the facies into a more energetic zone. The degree of wave action, however, was evidently insufficient to dominate over biogenic processes.

Facies C was deposited in the transition zone and lower shoreface environments as defined by Reineck and Singh (1980) and Howard and Reineck (1981). The problem in this interpretation is the fact that facies C is much thicker than the entire beach-to-shelf sequence observed in modern low wave-energy environments. However, for higher wave-energy environments, Howard and Reineck (1981) have shown that the entire shoreface and transition zone package is substantially thicker even though sedimentary sequences and characteristics remain the same. This unusual thickness (> 12 m: 39.37 ft) is evident in facies C and reflects the higher wave-energies associated with deposition at the shelf-margin.

The contact between facies C and D is a disconformity in the cored sequence and marks the initiation of a transgressive phase of deposition. The hiatus is reflected in the lack of upper shoreface and foreshore stratification in the cored sequence. The abundance of carbonate shell fragments and sand- size grains in facies D is associated with decreased sediment supply and a winnowing of fine-grained material.

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Facies E is glauconite-rich and bioturbated, thereby reflecting the dominance of biogenic processes. This facies represents deposition on a sediment-deficient shelf during a transgression. The shelf is probably below storm wave-base.

With the continued rise of relative sea level, facies F was deposited in deeper water on the shelf under conditions which were hostile to bottom- dwelling fauna. Although similar to facies A, this facies lacks the contorted bedding prevalent in facies A. Laminated siltstone lenses suggest episodic coarser-grained sedimentation. Facies F represents the culmination of the depositional event responsible for the formation of the W8 sandstone.

DEPOSITIONAL MODEL

Characteristics including geometry, lateral continuity, thickness of the sequence, and proximity to the shelf-margin suggest that the W8 sandstone represents a progradational shoreface sequence that formed at or near the shelf-edge (Fig. 2.22). The role of subsidence due to growth-faulting or sediment compaction cannot be dismissed as a possible mechanism for the development of such a thick lower shoreface sequence. However, it is equally likely that the thickness of the sequence reflects primary depositional control. Sand bodies forming at a shelf-margin are subject to much higher wave- energy than those forming on a broad shallow shelf where wave refraction and energy dissipation are greater. The two sandstone intervals underlying the W8

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WILCOX SHELF - EDGE DELTA MODEL

Figure 2.22 Block diagram depicting a paleogeographic reconstruction of the depositional setting for the W8 Sandstone, specifically a prograding shoreface system at the shelf edge.

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sandstone (Fig. 2.4) probably represent similar depositional events which indicates that the depositional episode is made up of three stacked prograding shoreface sequences. Since there is no direct evidence of a fluvial system associated with the sand body, the applicability of a shelf-edge delta model is debatable. Although it is implicit in the development of a progradational sequence at the shelf-edge that there must also be an associated fluvial system (Suter and Berryhill, 1985), the recognition of these features may be beyond the resolution afforded by the available subsurface data.

RESERVOIR QUALITY

Of the six sedimentary facies recognized in the Fordoche field study area, only two (B and C) are associated with any significant hydrocarbon production. The uppermost half of the burrowed and massive-appearing sandstone of facies C and the laminated sandstone interbeds of facies B display the highest permeability and porosity measurements as determined by core-piug data (Table 1 ). Hence, they potentially possess the best 'reservoir quality'. The laminated sandstone interbeds of facies B have the highest average permeability (10 to 98 md) and porosity (10% to 23%) values in the W8 sandstone (Fig. 2.23). Average oil saturation values for these beds is 15% to 23%. However, although these values are strongly suggestive of high reservoir quality, the sandstone beds of facies B are relatively thin and interbedded with non-permeable mudstones (Figs. 2.8, 2.23). Therefore, despite the intermittent high porosity and permeability values, facies B lacks reservoir homogeneity and continuity and is classified as relatively poor quality.

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■D CD N. SMITH JR. #8 C/) W Woter Saturation (% ) FORDOCHE FIELD 3O* 100 80 60 40 20 0 SP(mV) Resistivity (ohms-mVm) S onic (A T ) O il Saturation (% ) Porosity (% ) 0 20 40 60 80 100 15 0.1 30 20 10

FACIES " f , WATER _ FACIES "E' FACIES "O '

3 CD

FACIES " C 3.C 3" CD ■OCD I C 98md aO 3 FACIES "B " ■O O

FACIES "A "

O c ■o CD Figure 2.23 Reservoir characteristics and downhole electric log signatures for C/) cored sedimentary facies from the W8 Sandstone interval in the N. o" Smith Jr. #8 well. Petrophysical data is from core plugs. Note 3 extremely high permeability at the top of facies C and in the thin beds at 13,230 ft in facies B. o O) 107

Fades C is a burrowed and massive-appearing, very fine-grained sandstone. It has the highest overall reservoir quality and is the main producing interval within the W8 sandstone. Measured porosity values in facies C show minimal variation in the cored interval.of the N. Smith Jr. #8 and range from 15% at the base of the unit to a maximum of 22% at the top (Fig. 2.23). The permeability and overall reservoir quality of facies C appears to be controlled by the original depositional fabric of the sandstone, as there is a strong correlation between permeability trends and the degree of biogenic versus physicai sedimentary structures. The lower two-thirds of facies C (Cored interval; 13,195 to 13,223 ft) is a highly burrowed to bioturbated interval with average permeability values of 0.1 to 1.0 md (Figs. 2.8, 2.23). It seems likely that the high degree of biogenic reworking has altered the original depositional fabric of the sandstone. The silt and clay linings of the burrowed traces in this interval probably yield numerous small-scale permeability barriers. The upper one-third of facies 0 (Cored interval: 13,183 to 13,195 ft) is a massive-appearing sandstone with low-angle planar laminations and relatively few burrow traces. Average permeability values in this interval are 5 to 15 md (Fig. 2.23). This high degree of reservoir quality is apparently due to the lack of biogenic reworking. The reservoir quality of facies C is greatly enhanced by its consistency in thickness and lateral continuity of the sandstones within Fordoche field (Fig. 2.24). The lateral continuity yields a homogeneous and continuous (along- strike) reservoir.

Another important facies within the W8 sandstone interval is facies D. It is a well-cemented, calcareous, very fine-grained sandstone. Average measured porosity values of 4% in facies D are probably a product of the dissolution of

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very low average permeability values (< 0.1 md) (Table 1 ; Fig. 2.23). Facies D is a potential diagenetic seal for hydrocarbons. This facies immediately overlies the main reservoir unit (facies C) and is laterally continuous through out most of Fordoche field (Fig. 2.24). Therefore, its potential value as a diagenetic seal is enhanced.

CONCLUSIONS

1. The downdip uppermost Wilcox trend in south-central Louisiana, including Fordoche field, is coincident with the location of the lower Cretaceous carbonate reef trend and upper Cretaceous clastic shelf-margins. The position of the shelf-edge was maintained at least through deposition of the uppermost Wilcox.

2. Fordoche field is an important Wilcox oil and gas field which produces within a strike-oriented exploration trend that extends east to west in south- central Louisiana. The strike-oriented trend is associated with a paleo shelf-margin. Additional production should be found along this downdip trend.

3. On the basis of electric-log correlations and sedimentologic analysis of conventional cores, it has been proposed that deposition of the W8 sandstone occurred as a prograding shoreface at or near the shelf-edge.

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important. Many of these storm beds have the largest permeability and porosity values of the entire sequence. However, the high degree of burrowing and lack of vertical homogeneity reduce the potential of their reservoir quality.

ACKNOWLEDGEMENTS

The assistance of the personnel of the Sun Oil Company, especially Ms. Judy Melvin, Mr. Mark Gaby, and Mr. Charles Mayne who provided petrophysical data, well-logs and cores from Fordoche field is gratefully acknowledged. The Sun Oil Company is also thanked for granting permission to utilize the N. Smith Jr. #8 core for this workshop. The Atlantic Richfield Company is gratefully acknowledged for financial support to the senior author in the form of a fellowship. This manuscript is part of an in-depth regional Wilcox study being jointly conducted by the Basin Research Institute and Louisiana Geological Survey. Tory Eddins provided detailed information on the production history and reservoir engineering parameters of the W8 sandstone. Lori Nunn analyzed foraminiferal assemblages from mudstones overlying the W8 sandstone cored interval. The directors of the Basin Research Institute (C. H. Moore) and the Louisiana Geological Survey (C. G. Groat) are thanked for their continuous support and encouragement in this and other subsurface studies of the northern Gulf of Mexico.

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REFERENCES

Aigner, T., 1985, Storm Depositional Systems: Dynamic Stratigraphy in Modem and Ancient Shallow-Marine Sequences, Springer-Verlag, Berlin, 174 p. Albach, D. 0., 1979, The depositional history of the uppermost Wilcox (lower Eocene) of west-central Beauregard Parish, Louisiana: Baton Rouge, Louisiana State University, Master's thesis, 98 p. Anisgard, H. W., 1970, Causes of dominantly arenaceous foraminiferal assemblages in downdip Wilcox of Louisiana: Gulf Coast Assoc. Geol. See. Trans., v. 20, p. 210-217. Berg, R. R. and Tedford, F, J., 1977, Characteristics of Wilcox gas reservoirs, northeast Thompsonville Field, Jim Hogg and Webb Counties, Texas: Gulf Coast Assoc. Geol. Soc. Trans., v. 27, p. 6-19. Bourgeois, J., 1980, A transgressive shelf sequence exhibiting hummocky stratification-the Cape Sebastian Sandstone (upper Cretaceous), southwestern Oregon: Jour. Sed. Petrology, v. 50, p. 681-702. Brenchley, P. J., 1985, Storm influenced sandstone beds: Modern Geology., v. 9, p. 369-396. Busch, D. A., 1975, Influence of growth faulting on sedimentation and prospect evaluation: Am. Assoc. Petroleum Geologists Bull., v. 59, p. 217-230. Christina, C. C. and Martin, K. G., 1979, The lower Tuscaloosa trend of south- central Louisiana, 'You ain't seen nothing till you've seen the Tuscaloosa': Gulf Coast Assoc. Geol. Soc. Trans., v. 29, p. 37-41. Chuber, S. and Begernan, R. L., 1982, Productive lower Wilcox stratigraphie traps from an entrenched valley in Kinkier Field, Lavaca County, Texas: Gulf Coast Assoc. Geol. Soc. Trans., v. 32, p. 255-262.

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Coates, E. J., 1979, The occurrence of Wilcox lignite in west-central Louisiana:

Baton Rouge, Louisiana State University, Master’s thesis, 249 p. Craft, W. E., 1966, Channel sands are the key to Wilcox oil; Oil and Gas Jour., v. 64, no. 15, p. 124-130. Durham, C. O. and Peoples, E. M., 1956, Pleistocene fault zone in southeastern

Louisiana: Gulf Coast Assoc. Geol. Soc. Trans., v. 6, p. 65-66. Eckles, W. W., Jr., Prihoda, C., and Holden, W. W., 1981, Unique enhanced oil and gas recovery for very high-pressure Wilcox sands uses cryogenic nitrogen and methane mixture: Jour. Petrol. Tech., June, p. 971-983. Edwards, M. B., 1980, The Live Oak delta complex - an unstable shelf-edge delta in the deep Wilcox trend of south Texas: Gulf Coast Assoc. Geol. Soc. Trans., v. 30, p. 71-79. Edwards, M. B., 1981, Upper Wilcox Rosita delta system of south Texas: growth- faulted shelf-edge deltas: Am. Assoc. Petroleum Geologists Bull., v. 65, p. 54-73.

Fisher, W. L. and McGowen, J. H., 1967, Depositional systems in the Wilcox Group of Texas and their relationship to occurrence of oil and gas: Gulf Coast Assoc. Geol. Soc. Trans., v. 17, p. 105-125. Galloway, W. E., 1968, Depositional systems of the lower Wilcox Group, north- central Gulf Coast Basin: Gulf Coast Assoc. Geol. Soc. Trans., v. 18, p. 275-289. Hendricks, L. and Wilson, W. P., 1967, Introduction: In L. Hendricks, ed., Commanchean (Lower Cretaceous) Stratigraphy and Paleontology of Texas, Permian Basin Sec. Soc. Econ. Paleontologists Mineralogists Pub. No. 67-8, Midland, Texas, p. 1-6.

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Howard, J. D. and Reineck, H. E., 1981, Depositional facies of high-energy beach-to-offshore sequence - comparison with low-energy sequence: Am. Assoc. Petroleum Geologists Bull., v. 65, p. 807-830. Hoyt, W. V., 1959, Erosional channel in the middle Wilcox near Yoakum, Lavaca County, Texas: Gulf Coast Assoc. Geol. Soc. Trans., v. 9, p. 41-50. Jackson, M. P. A. and Galloway, W. E., 1984, Structural and Depositional Styles of Gulf Coast Tertiary Continental Margins, Application to Hydrocarbon Expioration, Am. Assoc. Petroleum Geologists Note Series No. 25, Tulsa, 226 p. Lehner, P., 1969, Salt tectonics and Pleistocene stratigraphy on continental slope of northern Gulf of Mexico: Am. Assoc. Petroleum Geologists Bull.,

V. 53, p. 2431-2479. Louisiana Geological Survey, 1981, Oil and gas maps of Louisiana: scale 1:380, 2 sheets, Baton Rouge, Louisiana. Lowry, P., Lemoine, R. 0., and Moslow, T. P., 1986, Shelf-margin sedimentation

in the Wilcox Group, south-central Louisiana (abs.): Am. Assoc. Petroleum Geologists Bull., v. 70, p. 1185. Martin, R. G., 1978, Northern and Eastern Gulf of Mexico continental margin: Stratigraphie and structural framework: in A. H. Bouma, G. T. Moore, and J. M. Coleman, eds.. Framework, Facies, and Oil-Trapping Characteristics of the Upper Continental Margin, Am. Ar.soc. Petroleum Geologists Studies in Geology no. 7, p. 21-42. McCulloh, R. P. and Eversull, L. G., 1986, Shale-filled channel system in the Wilcox, north-central south Louisiana (abs.): Am. Assoc. Petroleum Geologists Bull., v. 70, p. 1186.

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Mulcahy, S. A., 1981, Near-surface lignite occurrence, Sabine Uplift, northwest Louisiana: Baton Rouge, Louisiana State University, Master's thesis, 190

p. Pierson, J. R., 1970, Typical Oil and Gas fields of Southeast Louisiana, v. 2, Lafayette Geological Soc., Lafayette, Louisiana, p. 9-9g. Reineck, H. E. and Singh, I. B., 1980, Depositional Sedimentary Environments - With Reference to Terrigeneous Clastics, 2nd ed., Springer-Verlag, New York, 549 p.

Rogers, J. D., 1983, The occurrence of deep basin lignite in the Wilcox Group of northeast Louisiana; Baton Rouge, Louisiana State University, Master’s thesis, 165 p.

Self, G. A., Breard, S. Q., Rael, H. P., Stein, J. A., Traugott, M. O., and Easom, W. D., 1985, Lockhart Crossing field (abs.): New Wilcox trend in southeastern Louisiana: Am. Assoc. Petroleum Geologists. Bull., v. 69, p. 306.

Stehli, F. G., Creath, W. B., Upshaw, 0. F., and Forgotson, J. J., Jr., 1972, Depositional history of Gulfian Cretaceous of East Texas Embayment: Am. Assoc. Petroleum Geologists Bull., v. 69, p. 77-91. Suter, J. R. and Berryhill, H. L., Jr., 1985, Late Quaternary shelf-margin deltas, northwest Gulf of Mexico: Am. Assoc. Petroleum Geologists Bull., v. 69, p. 77-91.

Swift, D. J. P., Niederoda, A. W., Vincent, C. E., and Hopkins, T. S., 1985, Barrier island evolution, middle Atlantic shelf, U.S.A. Part l-shoreface dynamics: Marine Geol., v. 63, p. 331-361.

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Walker, R. G., 1984, Shelf and shallow marine sands: in R. G. Walker, ed., Facies Models, 2nd ed., Geosci. Can. Reprint Series 1, p. 141-170. Winker, 0. D., 1982, Cenozoic shelf margins, northwestern Gulf of Mexico: Gulf Coast Assoc. Geol. Soc. Trans., v. 32, p. 427-448.

Winker, 0. D. and Edwards, M. B., 1983, Unstable progradational clastic shelf margins: in D. J. Stanley and G. T. Moore, eds.. The Shelfbreak - Critical Interface on Continental Margins, Soc. Econ. P aleontologists Mineralogists Spec. Pub. 33, p. 139-157.

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SEDIMENTARY FACIES FROM A SHOREFACE SEQUENCE IN A STABLE SHELF-MARGIN SETTING: THE WILCOX GROUP (PALEOCENE - EOCENE), CENTRAL LOUISIANA

ABSTRACT

Conventional core data from a stable portion of an ancient shelf-margin provide valuable insight into the preserved sedimentary facies within this depositional system. The core data are from a relatively large, strike-oriented sandstone body which is over 65 km (40 mi) long, and in places is 16 to 23 km (10 to 14 mi) wide. Thickness of the sandstone interval is relatively uniform and averages between 9.1 to 13.7 m. (30 to 45 ft). In a previously published paper (Self et al, 1986), the authors interpret the sequence as representing a subaqueous shoai or 'nearshore marine bar' which lies seaward of a tidal flat complex. In contrast to the shoal model, this author's interpretation depicts a truncated progradational strandplain shoreface sequence overlain and underlain by shelf mudstones. Although the sandstone body occurs within a relatively stable region of the shelf-margin, evidence from well-logs and conventional cores show that some syndepositional normal faulting occurred. Fault motion led to some local thickening of mudstones across the fault plane; however, the movement had little effect on the thickness of the sandstone body. In the interpretation of Self et al (1986), activation along a growth-fault after deposition of the 'bar' resulted in

115

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the constriction of flow of iagoonal tidal channels and the creation of a scoured channel. In light of the proposed interpretation, this 'channel facies' has been re-interpreted to have formed either in response to a relative sea-level fall or density driven fiows. The net resuit is a small scale fan-like feature at the base of the growth-fault scarp. When the shoreface sequence is compared to one from a strongly growth-faulted portion of the margin, there is little difference in the overall thickness of the intervals. The apparent sharp basal contact of the shoreface sequence reflects an absence of a well-defined transition zone facies in the sandstone body located in the stable region of the margin. It Is proposed that the feature in the stable region formed during a sea-level fall coupled with an abundant sediment supply. Therefore, this study presents a facies model for a regressive shoreface sequence which has not been previously well- documented.

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INTRODUCTION

Sandstone bodies which have formed at or near the shelf edge have been the focus of attention in recent years as their potential as exceüent hydrocarbon reservoirs has been realized. Suter and Berryhill (1985) presented an excellent account of the seismic expression of shelf-margin deltas which formed during the last sea-level lowstand on the Louisiana and Texas continental shelves. Winker and Edwards (Winker, 1982; 1984; Edwards, 1980; 1981; and Winker and Edwards, 1983) presented several studies on the subsurface character of Gulf Coast Tertiary shelf-margin deltas. However, these studies were based exclusively on well-log and seismic data. Therefore, it becomes apparent that there is an absence of information on the sedimentary facies of shelf-margin depositional systems as observed in cores. Conventional core data from an important oil field associated with an ancient shelf-margin trend were examined in this study. These cores come from uppermost Wilcox (Paleocene-Eocene) rocks in the Lockhart Crossing field, Livingston Parish, Louisiana (Fig. 3.1) and, specifically, from the '1st Wilcox'

sandstone. These data provide a significant opportunity to gain insight into the nature of preserved sedimentary facies within the stable clastic shelf-margin. In addition, well-log data were used to examine the influence of syndepositional faulting on the development of sandstone bodies within this depositional system.

In a previously published paper. Self et al (1986) interpreted the '1st Wilcox' interval as representing a subaqueous shoal or 'nearshore marine bar' which formed during an overall regressive phase. In this paper, an alternate

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ADAMS FRANKUN

WILKINSON AMITE PIKE

W. FEUCIANA/ E FELICIANA ST. HELENA

[POINTE COUPEE TANGIPAHOA

ST LANDRY LIVINGSTON WESTd> EAST BATON BATON V ROUGE

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Gas * Dry If Abandoned^ Core location A

41

Figure 3.1 General location map of Louisiana and Lockhart Grossing field within Livingston Parish.

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model depicting a truncated progradational shoreface sequence overlain by shelf muds is presented. In the subsurface, where there is often limited core data available, it is possible that the truncated shoreface sequence may appear to be morphologically and sedimsntologically similar to some shelf-shoai facies models. Therefore, an objective of this paper is to present criteria which will facilitate the distinction between truncated shoreface and shelf-shoal sequences.

A perspective of the '1st Wilcox' interval in relation to regional Wilcox stratigraphy in Louisiana will be presented in this paper. An examination of two important aspects of the truncated shoreface sequence will subsequently be presented. These aspects are: a) preserved lithofacies, and b) the effect of growth-faulting on the development of the depositional feature. The facies sequences of the truncated shoreface are then contrasted with those for shelf shoals. Finally, criteria which may be used to distinguish these two features in the subsurface, where limited core data are available, are presented.

WILCOX DEPOSITIONAL SEQUENCES

General backoround

The Wilcox Group represents the incipient stage of Tertiary fill of the Gulf coast basin and reaches a maximum thickness of 1219 m (4000 ft) within the Louisiana subsurface. Two distinct oil and gas production trends are recognizable within the state. The first trend is located in the northern part of the state and is primarily dip-oriented. The second trend extends east-west through

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shelf-margins. The second trend (hereafter referred to as the Wilcox shelf- margin trend) defines the basin ward limit of the main Wilcox sandstone facies. Lowry (Chapter one) has shown that the subsurface Wilcox shelf-margin trend in central Louisiana is comprised of at least seven major depositional sequences. Each sequence is bounded by a regional transgressive mudstone interval. The mudstones interfinger with sandier lithofacies updip and merge into basinal facies downdip. No exact age ranges for the sequences are available; however, on the basis of the duration of Wilcox deposition (~7 to 8 me) and the number of sequences, it is likely that they are comparable to third

(106 to 107 years) or fourth-order (104 to 10® years) global sea-level cycles as described by Vail et al (1977).

The vertical arrangement of depositional sequences within the Wilcox shelf-margin trend is shown in figure 3.2. It is apparent that there has been relatively little migration of the most basinward extent of the sequences from their original downdip location. One may conclude that this pattern reflects an equilibrium between sediment supply, subsidence, and high order relative sea- level change.

Stratigraphie relationships of the '1st Wilcox' depositional event

This study is focused on a depositional event which occurs within the final Wilcox depositional sequence W-VII. This sequence is comprised of at least five other depositional events (Fig. 3.3). Down-dip, the boundaries between individual events in this area are relatively easy to identify. Up-dip,

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however, they become progressively more difficult to recognize as the transgressive mudstone facies pinches out.

Figure 3.4 is a net sandstone map of the lower half of sequence W-VII which depicts the maximum limit of sandstones occurring within the central region of Livingston Parish. In comparison, figure 3.5 is a net sandstone map for the upper half of the sequence. Two important differences between figures 3.4 and 3.5 are revealed. First, the down-dip limit of the main sandstone facies in the upper half of the depositional sequence has been translated 32.25 to 40.3 km (20 to 25 mi) landward from that of the lower half. Secondly, a well-defined strike-oriented sandstone body in the upper half is located 32.25 km (20 mi) downdip from the limit of the main sandstone facies. The localized occurrence of sandstone in the upper half of the sequence in East Feliciana Parish (Fig. 3.5) represents deposition associated with the final depositional event. This deposit is genetically unrelated to the underlying and downdip strike-oriented feature (Fig. 3.3).

Geometry of the '1st Wilcox'

Figure 3.6 is an isopach map of the '1st Wilcox' sandstone interval in the study area. The map shows that the interval thickness averages 9.1 to 13.7 m (30 to 45 ft). The sandstone interval can be traced over 65 km (40 mi) along strike, and up to 23 km (14 mi) updip. A series of cross-sections through the feature reveals that this sandstone body has an assymetric profile with the steepest face occurring in the basinward direction (Fig. 3.7).

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In comparison with the morphology of some other 'strike-oriented sand bodies', the '1st Wilcox' sandstone body is a relativeiy large feature. The '1st Wilcox' is at least twice as wide as the Galveston Island shoreface sequence and, while similar in length and width to Ship Shoal, it is more than twice as thick.

FACiES OF THE '1ST WILCOX' SANDSTONE

The following is a description of the facies observed in the cores within this interval.

Facies 'A'

Facies A is a mudstone characterized by the relative absence of bioturbation (<5%) and the occurrence of thin (5 to 10 cm: 1.95 to 3.9 in) very fine sandstone beds. The mudstone shows distinct laminations and minor occurrences of soft sediment deformation. The silt-sized component averages 30 to 40%, increasing slightly toward the main sandstone interval. Traces of pyrite {<1 to 2%) occur throughout the unit and may be locally concentrated along bedding planes. Minor traces of glauconite (<1%) occur throughout the interval and are mainly associated with small (0.5 to 1.0 cm; 0.195 to 0.39 in) silt-filled ovate burrows. Some burrows contain pelecypod fragments and occasionally exhibit faint spreiten.

Most discrete sandstone beds (average grain size 75-120 pm) exhibit horizontal planar tabular laminations (Fig. 3.8); however, some contain well-

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Figure 3.8 Close-up view of a sandstone interbed within facies A. Note the horizontal laminations throughout the bed and the occurrence of Planolites burrows near the upper contact.

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defined ripple cross-laminations. These ripple-bedded sandstones appear to have resulted from the migration of wave ripples, rather than large scale unidirectional current generated bedforms. The lower bounding surfaces of the laminasets tend to be irregular. In areas where they have been preserved, the basal and upper contacts of these sandstone beds are very sharp with almost no evidence of burrowing. The degree of burrowing throughout this entire facies is significantly low. The burrows that are distinct occur close to the lower contact of the main sandstone facies and are primarily sandstone-filled ovate forms (Planolites). There are some rare occurrences of Telchinus and Terebelllna burrows. Benthic foraminifera from the mudstone indicate an inner-neritic to middle-neritic environment (Table 3.1). Figure 3.9 shows how the number of sandstones per meter of cored interval increases upwards toward the contact with the overlying sandstone. There is no evidence of amalgamation of these beds.

Facies B

Facies B constitutes the main resen/oir sandstone. It is an extensively burrowed, very fine-grained sandstone (average grain size 100 to 125 pm). The sandstone shows very little variation in grain size from the base to the top of the interval; however, the percentage of mud present within the facies decreases toward the upper contact. The basal contact with the underlying mudstone appears sharp. The upper contact is also almost exclusively sharp.

Ophiomorpha burrows are abundant throughout the lower half of the interval and, with the exception of the upper 50 cm (19.5 in), the entire

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Fauna Environment

Robulus americanus Middle shelf Cibicides sp. Middle shelf to lower slope Uvigerina peregina Middle shelf to upper slope Robulus sp. Middle shelf to upper slope Hapiophragmoides sp. Lower slope Ammobaculites sp Inner shelf Nonion sp. Inner shelf

Table 3.1. Benthic foraminifera from faoies A.

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10202.5 10207 J 10210.5 ■S 10216 g^ 10216.5 10239.5 Gallon, A. Thom #1 10243 10246.5

0 10 20 Number of storm-beds per three foot interval

10110.000 10112.500 10115.500 X 0118.500 ^ 0121.500 0124.500 10127.500 Lease 7729 #1 10130.500 10133.500 —I------1------1------1------1— 0 10 20 30 Number of storm-beds per three feet interval

10630 10633 10638

g 10642 S 10645 10648 10651 SUN Crown Zelierbach 10654 10657

} 1 2 3 4 5 G Number of storm-beds per three ft. interval

Figure 3.9 Frequency of beds greater than 1 cm thick in facies A with depth. a) A. Thom #1 b) State Lease 7729 #1 c) Crown Zelierbach #1

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sandstone interval is extensively bioturbated. No other distinct burrow types are visible within the bioturbated interval. Physical sedimentary structures within facies B are rare; however, three bedding types were observed. First, in the A. Thom #1 core (Fig. 3.10), a thin (5cm: 1.95 in), fine to medium-grained sandstone (200-225pm) bed occurs within the bioturbated sandstone. The bed contained disarticulated shell debris and both the upper and lower contacts were sharp. An x-ray radiograph (Fig. 3.1 la) shows that while the bed appears to be well burrowed, some shell debris is aligned along faint horizontal laminations. The second physical sedimentary structure which occurs within the main sandstone is horizontal planar tabular laminations. There are two separate locations in the interval where this bedding type occurs. The most frequent location is near the upper contact with the overlying facies. This component of facies B is associated with a decrease in the degree of burrowing. In the #1 Morrison core (Fig. 3.11b), small (1 cm: 0.39 in) sub-angular to sub-rounded mudstone clasts appear to be aligned along these bedding planes. Figure 3.12a is an x-ray radiograph showing the other less frequently preserved bedding type within the main sandstone interval. This bedding type occurs within the lower portions of the main bioturbated sandstone and is only apparent where biogenic activity is low. The third bedding type was observed within the #1 Sullivan core (Fig. 3.12b). This photograph shows an example of trough cross-stratification occurring within the lower portion of the bioturbated facies. In over 300 m (984 ft) of cores examined, this was the only occurrence of this bedding type within the bioturbated sandstone.

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10,130 flllltfiif FACIES C

1 0 ,1 4 0 -

1 0 ,1 5 0 - FACIES E

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1 0 ,2 6 0 -I Figure 3.10 Schematic core description of the A. Thom #1 core. Note the missing core intervals. Also note how facies E unconformably overlies facies B,

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Figure 3.11 a) X-ray radiograph of a medium sand-sized bed which occurs within facies B. b) Close-up photograph of small mudstone clasts which occur near the upper contact of facies 8.

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I

:i-

Figure 3.12 a) X-ray radiograph of rare horizontal laminations which occur within facies B. b) Close-up photograph of extremely rare trough cross-stratification from facies B.

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Facies C

Immediately overlying the main sandstone is a mudstone which is highly variable in appearance. In some cores, distinct horizontal laminations were evident in the overlying mudstone (Fig. 3.13a). However, the mudstone was extensively burrowed in other cores (Fig. 3.13b).

Characteristic features of this facies include the absence of discrete siltsone beds and the fact that its total thickness rarely exceeds 1 m (3.2808 ft). This facies is similar to facies A in that benthic foraminifera from the mudstone indicate an inner-neritic to middle-neritic environment (Table 3.2).

Facies D

Facies D is a matrix-supported, disorganized, poorly sorted conglomerate (Fig. 3.14). Clast size ranges from 10 cm to 0.5 cm (3.9 to 0.195 in). Clast shape ranges from angular to well-rounded. Grain size of the sandstone matrix averages 125-150 pm. Clasts are randomly arranged and do not show any degree of imbrication. However, in a few instances where clast size is small (< 1 cm (0.39 in) in diameter), they may be aligned along horizontal planar tabular bedding planes. These clasts are composed of thinly laminated mudstones most of which exhibit the original primary sedimentary structures (Fig. 3.14). These structures include small connected and disconnected siltstone lenses and streaky laminations. There are no recognizable biogenic structures associated with this facies.

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* î l

Figure 3.13 a) Close-up photograph of horizontally laminated mudstone of facies C. b) Close-up photograph of facies 0, this time showing how extensively burrowed the facies may appear.

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Fauna Environment

Robulus americanus Middle shelf Eponides sp. Outer shelf to upper slope Uvigerina peregina Middle shelf to upper slope Ammobaculites sp. Inner shelf

Table 3.2. Benthic foraminifera from facies C.

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Figure 3.14 Close-up photograph of the O. M. Barnett core. Note facies B and D and the appearance of relatively large angular mudstone clasts. Note the range in size of mud clasts and the preservation of internal bedding within the clasts.

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1 ^ 0 '^94j ■ssamÉÉesssseeÉâ

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Facies E

Facies E is characterized by an abundance of wave and current generated physical sedimentary structures. These structures include horizontal laminations; moderate to high angle (10 to >20°) planar tabular laminations; tangential tabular laminasets; and wavy and flaser bedding (Fig. 3.15). Average grain size of the facies is 125 to 150 |im with a maximum of 250 pm. Two distinct biogenic sedimentary structures were observed within this facies. These structures are: a) an oblique, sand-filled burrow, with mud-lined walls (Fig. 3.16a), and b) a vertical sand-filled burrow containing fecal pellets (Fig. 3.16b). The latter burrow can only be observed in an x-ray radiograph where the sediment surrounding the burrow nucleus is bent downward.

PREVIOUS INTERPRETATION

The following is a summary of the depositional model for the '1st Wilcox’ sandstone within the Lockhart Crossing field presented by Self et al (1986). Their model depicted a subaqueous shoal or 'nearshore marine bar' lying seaward of a tidal-flat complex and was referred to as a 'bald barrier island'. Inferred time-lines within the shoal suggest progradation into progressively deeper water. Migration of tidal channels landward of the shoal was believed to be responsible for the erosion of the upper portions of the sequence. A channel which transects the shoal was believed to have formed as a result of activation of a regional growth-fault. However, description of the

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Figure 3.15 Close-up photographs of bedding types from Facies E.

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Figure 3.16 X-ray radiograph of burrows from facies E near the contact with facies B. a) Oblique sand-filled burrows with mud-lined walls. b) Vertical sand-filled burrows. The white specks depict glauconite pellets within the burrow-fill. Note how the surrounding laminae have been bent downward by the burrowing organism.

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processes which were responsible for the channelization and deposition of the channel-fill are extremely vague. They proposed that tidal flow associated with the lagoon was 'restricted as a result of extension along the fault'. Constriction of the flow led to localized scouring and erosion of the 'bar' facies. The channel migrated northward and incised 'lagoonal' and 'bar' facies. Several observations made in this study suggest an alternate model for both the origin of the 'bar' and 'channel' facies to that proposed by Self et al (1986). The two fundamental differences between the models concern the origin of the overlying mudstone and the origin of the channel facies. These differences are outlined below.

SHELF VERSUS LAGOONAL MUDSTONES

Introduction

An important component in the interpretation of Self et al (1986) was that the mudstones overlying the main sandstone interval represent deposition in a lagoonal environment. This conclusion was based primarily on the presence of characteristic benthic foraminifera. In contrast, in the interpretation presented here, the mudstones which overly the main sandstone are believed to have been deposited as shelf muds and represent the transition between two distinct depositional events (Fig. 3.3). The following is an examination of three key attributes which were used to conclude that the overlying mudstones originated on the shelf rather than lagoonal environment.

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Micropaleontoloaical evidence

Self et al (1986) used the presence of the arenaceous benthic

ioravnlnliera Ammobaculiiessp., Trochammania sp. and Haplophragmoides sp. within the overlying mudstones (Facies A and C) to indicate deposition in a lagoon or open bay. However, samples examined for this study revealed that while present, these species occurred with several other foraminifera which suggest deposition on an inner to middle shelf setting. It is likely that these foraminifera were transported from shallow water by the offshore-directed storm flows during the transgression of the main shoreface (Facies B). During storms, sediment is transported from the shoreface onto the shelf and, therefore, organisms within these sediments may be redeposited into deeper water, it therefore becomes apparent that the use of micropaleontologlcal evidence in the absence of an understanding of the surrounding facies and the processes which formed them, may result in a misinterpretation of the depositional environment.

Biogenic activitv

The lagoonal or back barrier setting is characterized by a high degree of organic productivity (Howard and Frey, 1985). This activity may present itself as the ubiquitous occurrence of root casts or localized lignitic horizons throughout the mudstone. In humid climates, Zostera and Spartina are two common floral components found in backbarrier settings, while mangrove swamps dominate the tropical and sub-tropical climates. Each of these flora have the potential to

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There was no evidence of concentrated Intervals of organic debris or root casts In any of the overlying mudstones that were examined.

The backbarrier setting may also be characterized by an abundance of brackish water macroinvertebrate shells (Relneck and Singh, 1980). However, there was no evidence of brackish water lamelilbranchs or other back-barrler fauna, either articulated or disarticulated. In any of the cores examined. The mudstone Immediately overlying the '1st Wilcox' exhibits a variety of burrowing activity (Fig.3.13). For the most part, the overlying mudstones have a mottled appearance and distinct burrows are rare. It would be unwise to use the presence or absence of certain Ichnofosslls to discriminate between shelf and lagoonal/backbarrler mudstones because It Is clear that several forms may occur In both environments. However, the absence of a large floral and macrofaunal component suggests a shelf setting Is more likely than a lagoonal one.

Vertical Sequence

In stating that the overlying mudstones up to the top of the Wilcox are lagoonal. Self et al (1986) Infer that the depositional feature at Lockhart Crossing occurs within an overall regressive sequence. The vertical profiles of

regressive and transgresslve shoreface sequences have been well documented (Bernard et al, 1959; 1962; Curray et al, 1969; Kraft, 1971 ; Kraft et al, 1973; Relneck and Singh, 1971 ; 1980; Carter, 1978; Elliot, 1978; Roep et al, 1979; Demarest et al, 1981 ; and Tavener-Smlth, 1982).

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stressed in recent reviews {Heward, 1981; Reinson, 1984; and Miall, 1984) that the Galveston Island vertical profile merely represents an end member in a continuum of shoreface sequences, the general sequence is still a valid and applicable model. In a completely preserved regressive shoreface sequence, nearshore sediments overly shelf muds, and backbarrier muds rich in organics overly the main shoreface sands (Tavener-Smith, 1982). Near the toe of the shoreface, shelf muds overly the sand facies. The complete regressive sequence is not, however, always preserved because of either tidal inlet migration or erosional shoreface retreat (McCubbin, 1982). There is an important distinction between the stratigraphie sequences produced in a regressive system which is undergoing erosion by tidal inlet migration versus one subjected to erosional shoreface retreat. In the tidal inlet model where back barrier tidal channels erode the shoreface sands, a barrier must still exist seaward of the lagoonal facies (Fig. 3.17a). In the erosional shoreface retreat model, the upper shoreface, beach and lagoonal facies (if present) are eroded and overlain with shelf muds (Fig. 3.17b). Therefore, the vertical profile depicts a truncated shoreface sequence overlain by shelf mudstones which merge with basinal facies downdip. In the model presented by Self et al (1986), the authors state that the mudstones which occur in the interval (24.4 to 30.5 m; 80 to 100 ft thick) between the top of the '1st Wilcox' and the top of the Wilcox Group represent lagoonal or open bay sediments. This implies that a barrier of a thickness comparable to that of the mudstone interval must occur basinward of the

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Swamp

Tidal Flats & Lagoon onshore

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B Barrier Thin salt marsh peat

/ / LoQoon mud -

Retrograded barrier Thick satt marsh peat Nearshore marine sediments

Logoon mud

Figure 3.17 Depositional models for the transgressed shoreface sequence. a) Erosion of shoreface by tidal inlets and back-barrier channels. (After Reinson, 1984). b) Erosional shoreface retreat model. (After Swift, 1968).

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Lockhart Crossing field. Examination of a regional cross-section (Fig. 3.3) shows that this situation does not occur.

In light of the above conclusions, these three lines of evidence (micropaleontologlcal, biogenic and vertical sequences) do not support the lagoonal mudstone model. Consequently, the conclusion that the '1st Wilcox' occurred within an overall regressive system is unsubstantiated. Conversely, these data demonstrate that at least one transgresslve event occurred after deposition of the '1st Wilcox' interval. This finding significantly alters the interpretation of the sequence.

CHARACTER OF THE CHANNEL FACIES

Self et al (1986) suggest that the channel facies which transects the main sandstone interval originated when activation of a regional growth-fault created localized scouring within the 'lagoonal' and 'bar' facies. The following description of the general morphologic and sedimentologic characteristics of the channel-fill facies will help establish the basis for an alternate model. A dip-oriented well-log cross-section (Fig. 3.18) through the probable axis of the channel depicts the relationship between the channel facies and fault motion as described by Self et al (1986). The sequence of events were: a) formation of the channel after deposition of the main sandstone interval (facies B) and the overlying mudstones (facies C and A); and b) deposition of the channel-fill following fault motion.

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Figure 3.18 Dip-oriented well-log cross-section through the probable axis of the channel system which transects Lockhart Crossing field. (See Fig. 3.1 for location).

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Maximum depth of the channel Incision Is 21.3 to 24.4 m (70 to 80 ft) although the average depth Is 12.2 m (40 ft). The feature extends at least 6.5 km (4 ml) updip from Lockhart Crossing field. A strlke-orlented well-log cross- section (Fig. 3.1 S) through the Interval reveals that channel width ranges from 0.62 to 0.93 km (1 to 1.5 ml). In most cases, the width to depth ratio of a tidal Inlet sequence would be much greater than that described above (Hoyt and Henry, 1967). Therefore, from a morphological standpoint, the channel system at Lockhart Crossing shows little resemblance to modern preserved tidal Inlet systems. Figure 3.20 depicts facies relationships within the channel. It also shows that unidirectional current ripple laminations occur In medium-grained sandstones near the base of the channel. UpdIp of the fault, erosion has removed almost all of the underlying sandstone. The channel-fill facies Is dominated by wavy and flaser-bedded fine sandstones. Downdip from, but closest to the fault, the physical sedimentary structures of the channel-fill range from current llneatlons with small, well-rounded mud clasts aligned on bedding planes near the base to large angular mud clasts that are randomly arranged within a sand matrix. Intermittent occurrences of horizontal planar tabular and small trough cross-bedding separate the large mud clast Intervals. The size and frequency of clasts decrease toward the upper contact and small trough cross and flaser bedding predominate. Less than 300 m (984 ft) downdip from the fault, there are only a few occurrences of small mud clasts within the channel and the sequence Is dominated by current-generated ripple and wavy bedding. Some localized soft sediment slumping Is evident. At this location, however, the channel barely

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Figure 3.19 Strike-oriented well-log cross-section through the probable axis of the channel system which transects Lockhart Crossing field. (See Fig. 3.1 for location).

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incised the underlying sandstone and, in fact, 8.7 m (28.5 ft) of sandstone belonging to facies B underly the channel-fill. Downdip, there is no evidence of facies D or E truncating the main sandstone or occurring in the overlying mudstones. The character and relationship of this channel to the '1st Wilcox' will be discussed in the following section.

PROPOSED DEPOSITIONAL MODEL

Introduction

The following is a proposed depositional model for the '1st Wilcox'. This model is based on processes inferred from observations in cores in addition to the relationship of the interval to regional Wilcox paleogeography. A representative vertical profile through the main interval is described below.

Vertical sequence

Facies A is an interbedded mudstone which is believed to represent an inner to middle shelf depositional setting. Mudstones of this interval contain inner to middle neritic benthic foraminifera and can be seen to merge with basinal mudstone facies downdip. Individual very fine sandstone beds represent deposition from seaward directed storm flows. There is, however, a paradox in regards to the 'shelf mudstone'. In many other shelf sequences which have been described in the literature (Reineck and Singh, 1980; Boyles et al, 1981 ; Tillman and Martinsen, 1984; Tye et al, 1986; Kofron, 1987), one of

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burrowing and relative diversity of burrowing organisms. Most cores examined within the study area show that burrowing is either absent or negligible. This lack of biogenic activity has been noted elsewhere within the Wilcox section (Anisgard, 1970) and is believed to be indicative of a relatively oxygen-deficient neritic environment. High rates of mud deposition from associated fluvial systems may also result in the predominance of physical structures over biogenic structures. The major reservoir facies is an extensively burrowed, fine-grained sandstone (facies B) which shows little variation in grain size in the vertical profile. The facies exhibits physical and biogenic sedimentary structures most commonly found in the lower to middle shoreface environment (Reineck and Singh, 1980). A medium-grained sandstone bed within the main fine-grained sandstone represents a proximal or shoreface storm layer, and is the landward counterpart of the very fine-grained sandstone beds characteristic of facies A. The occurrence of trough cross-bedding within the main sandstone probably resulted from the migration of nearshore bars (Davidson-Arnott and Greenwood, 1976).

There was no evidence of low to high angle discordant planar tabular laminations near the upper contact of the main sandstone facies in any of the cores examined. The occurrence of this bedding type may be used as evidence to support the interpretation that this portion of the sequence represents beach facies. The upper contact in every core examined is characterized by the preservation of horizontal, planar tabular laminations with a decrease in both the degree of burrowing and percentage of mud present. It is likely that the subaerial component and the upper portions of the shoreface were removed

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sandstone interval represents the reworking and redepositional phase associated with the ensuing transgression.

Facies C which directly overlies the main reservoir sandstone represents the deposition of shelf muds during the accompanying relative rise in sea-level. This facies is, in turn, overlain by facies A which is the interbedded mudstone. Facies A represents the initiation of the next depositional event. This vertical profile is essentially the same as one for a prograding shoreface sequence; however, only the lower portions of the sequence have been preserved. A modern analogue for this system must take the relatively large dimensions of the sandstone body into account.

Modern analogue

The beach ridge plain on the coast of Nayarit, Mexico (Curray et al, 1969) and the beach ridge complexes in the Tabasco region of Mexico (Psuty, 1966) are considered to be appropriate modern analogues for the '1st Wilcox' interval (Fig. 3.21), These relatively large sandbodies form a laterally extensive sand- sheet and, in the case of the Nayarit complex, are underlain by shelf muds. A stratigraphie section for the Nayarit beach ridge plain shows that the shoreface sequence is close to 10 m (32.8 ft) thick and is up to 15 km (10 mi) wide in places (Fig. 3.22). The beach ridge plain has formed adjacent to relatively small scale fluvial systems. Individual ridges are relatively low relief features (< 1 to 2 m: 3.28 to 6.56 ft) and occur landward of a lagoonal system.

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a

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RIVERS Of r iif CENTRAL UHAiriAGl BASIN

Figure 3.21 Probable modern analogues for the '1st Wilcox' interval at Lockhart Crossing. a) Coast of Nayarit, Mexico: a regressive strandplain complex (After Curray et al, 1969). b) Tabasco beach ridge complexes, Mexico. (After, Psuty, 1966).

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It is easy to envisage how such a depositional setting could have occurred at the Wilcox shelf-margin during deposition of the '1st Wilcox'. During

a relative lowstand of sea-level, numerous small fluvial systems would have occurred on the exposed continental shelf, thereby resulting in a high terrigenous influx to the shelf-margin. Where incident wave energy dominated over fluvial processes, extensive beach ridge plains would have formed adjacent to these small distributaries. As sediment supply to the system diminishes and/or relative sea-level begins to rise, the beach ridge complex is transgressed and the upper portions of the beach ridges are truncated by erosional shoreface retreat. Therefore, the depositional model of the '1st Wilcox' described above documents the preserved stratigraphie sequence of a transgressed beach ridge plain. According to Fischer's (1961) model for the preservation of coastal facies, the rate of sea-level rise would have been quite rapid.

Channel facies

In contrast to the model of channel formation of Self et al (1986), the model proposed in this paper depicts deposition in the form of a 'small-scale fan'-like feature. After the transgression of the strand plain shoreface, shelf muds were deposited on top of the main shoreface sands. As sea-level continued to rise, a localized trough developed in response to movement along a regional growth-fault. There are at least two possible explanations to account for the formation of the channel. First, it is possible that density-driven currents developed as

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these currents carried material basinward, the sudden change of slope at the base of the scarp would have resulted In the deposition of coarser-grained material close to the fault and led to the formation of a small fan-like feature (Fig. 3.23). Within the channel near the base of the fault scarp, debris flow sediments predominate and localized scouring is pronounced. Distal to the fault, the lack of large clasts and predominance of current structures suggest a reduction in flow strength. Once the channel was initiated, retrogressive slumping would have resulted in the migration of the channel updip. Migration, in turn, would have continued until an equilibrium profile was achieved. The wavy-bedded and flaser-bedded channel facies updip from the fault testify to the presence of alternating flow regimes. This model accounts for the rapid pinch-out of the 'channel facies' downdip in addition to the localized scoured-zone at the base of the fault scarp (Fig. 3.19).

The second explanation is comparable to the first in that both models result in the formation of a small-scale fan-like deposit at the base of a fault scarp. However, the driving mechanism for the development of the channel and channel-fill in the second model may have been related to a relative sea-level lowstand. This sea-level lowstand would have been associated with the subsequent depositional event (see Fig. 3.3). In this model, fluvial channels flowing across exposed shelf muds would deposit locally-derived sediment at the base of the subaqueous fault scarp, thereby leading to the development of

the small-scale fan. There appears to be little evidence in the cores, such as an oxidized zone, which supports the concept of a sea-level fall which would have sub-aerially exposed shelf muds. However, it is likely that such a zone may

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Figure 3.23 Schematic diagram depicting deposition of facies D and E within Lockhart Crossing field.

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have been obliterated during the subsequent transgression; therefore, this explanation must remain a possibility. The potential for the occurrence of these channel facies in other regions of the 1st Wilcox sandstone would appear greater if they formed in response to a sea-level fall

COMPARISON WITH A GROWTH-FAULTED MARGIN

When the stratigraphie sequence from the stable region of the shelf- margin (Lockhart Crossing) is compared to one from the unstable region (Fordoche field) (Chapter two), they appear to be quite similar. The main sandstone intervals within each depositional event are equal in thickness to each other, and exhibit similar physical and biogenic sedimentary structures. However, significant differences occur between these two sequences. The first difference concerns the underlying tempestites. At Fordoche field, these beds exhibit a distinctive increase in thickness and frequency toward the upper contact with the overlying sandstone (Fig. 3.24). Several of these tempestites are amalgamated near the upper contact of the main sandstone facies. This pattern is characteristic of the transition zone in a prograding shoreface sequence (Aigner, 1985; and Brenchley, 1985). Tempestites observed in cores from Lockhart Crossing, however, show an upwards increase in frequency (Fig. 3.9), but do not exhibit amalgamation. The lack of these amalgamated beds results in the appearance of a relatively sharp contact between the sandstone and mudstone interval. In the unstable shelf- margin, these storm beds are extensively bioturbated near their upper contacts and recognition of internal stratification is quite difficult. However, the underlying

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storm beds at Lockhart Crossing exhibit relatively little biogenic activity and the internal laminae are well preserved. The second major distinction between these two sequences concerns the intensity and diversity of biogenic activity within the shelf mudstones. In the unstable region, these mudstones are extensively bioturbated over a 5 m (16.4

ft) interval. Conversely, the burrowed mudstone interval in the stable region is confined to less than 0.5 m (1.64 ft). Additionally, the diversity of distinct burrow types is lower in the stable region of the margin. The well-developed carbonate lag which represents the 'ravinement surface' at Fordoche is not present at Lockhart Crossing. These differences in the facies sequence between two structurally distinct regions of the Wilcox shelf-margin may be a reflection of local variability in biogenic activity and depositional rates. It is equally likely, however, that the relatively sharp basal contact in the stable region, in contrast to the gradational contact in the unstable region, may reflect a significant difference in depositional style. Heward (1981) discusses the depositional style of regressive

shoreface sequences under variable sea-level conditions. In the classic 'Galveston Island' model, regression occurs during a rising sea-level due to excess sediment supply. Heward (1981) proposed that a regression occurring during sea-level fall will result in a significantly different stratigraphie sequence. The main difference between this regressive model and the Galveston model is a relative absence of transition zone facies and subsequent appearance of a sharp basal contact. Subaerial erosion of the updip regions of the shoreface sands results in the formation of a wedge-shaped sandstone 'package'.

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in eustatic sea-level which occurred during the two separate depositional events or increased subsidence within the unstable margin. It is probable that increased subsidence associated with growth-faulting in the unstable region could create a 'relative sea-level rise'. The resulting shoreface sequences would appear similar to the Galveston model. On the other hand, local subsidence would be less pronounced on the stable margin and a eustatic sea-level fall would result in a rapid basinward translation of coastal facies. The migration of the shoreface may have been so rapid that the potential for amalgamation of storm beds would be limited. Lowry (Chapter four) has numerically simulated hypothetical progradational shoreface sequences under a variety of sea-level changes.

On the basis of the simulations (Chapter four), it is concluded that the facies sequences described at Lockhart Crossing depict a prograding shoreface sequence which formed during a falling sea-level. Hence, the sequence described at Lockhart Crossing may serve as a valuable model for the recognition of similar features in the rock record.

SHELF SHOAL VERSUS TRUNCATED SHOREFACE

In referring to the '1st Wilcox' as a 'shoal'. Self et al (1986) imply that the feature formed in response to specific shelf processes and would therefore exhibit a characteristic vertical stratigraphie sequence. A number of vertical facies profiles which describe the general character of sand bodies occurring on the continental shelf have been presented. The similarity of some models to a truncated shoreface sequence means that, in practice, distinction of these

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processes responsible for the formation of shelf shoals and the facies sequences associated with them, several criteria which may facilitate the distinction between truncated shoreface and shelf shoals become apparent. There are two major mechanisms by which shoals may form on a continental shelf; a) submergence of an existing barrier complex, and b) transportation of shoreface sediments into deeper water leading to the development of a shoal.

Within the submergence category, there are two subdivisions: i) in-place drowning (Sanders and Kumar, 1975), and ii) transgressive submergence (Penland and Boyd, 1985). Johnson (1919) recognized the potential for barrier island submergence (in-place drowning) as a means to generate shoals on the continental shelf. Sanders and Kumar (1975) suggested that numerous shoals on the Long Island continental shelf formed in this manner. Lowry et al (1985) presented evidence to suggest in-place drowning of a low-profile gravel barrier system in the Alaskan Beaufort Sea. Penland and Boyd (1985) have been strong advooators of the transgressive submergence model, citing the inner-shelf shoals associated with the modern Mississippi delta complex as case examples. In the transgressive submergence model, a barrier system associated with a deltaic headland is submerged as the fluvial axis switches and sediment supply is cut off. As relative sea-level rises, the shelf sandbody moves landward and erosional shoreface retreat reworks the shoreface sediments. In terms of the preserved sandstone body, there is a clear distinction between a shoal formed by in-place drowning and one formed by transgressive submergence. Sandbodies formed by in-place drowning are overlain and

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Transgressive submergence, however, creates a disconformlty at the base of the sand interval as the feature migrates landward over lagoonal or inter-deltaic sediments. Preserved sandstone body geometry and internal stratification of shoals formed by transgressive submergence reflect extensive reworking and bear little resemblance to their original characteristics (Penland and Suter, 1986). Unless rapid burial occurs, the sandbody may be completely obliterated leaving only a thin sand sheet on the continental shelf. Within the second mechanism (transportation of shoreface sediments into deeper water), there are also two subdivisions: i) transportation of sediment from the shoreface through erosional shoreface retreat (Swift, 1968; Swift and Field, 1981), and ii) transportation of sediment from a deltaic source to produce a 'Shelf Plume' (Patterson, 1983; Palmer and Scott, 1984). In the erosional shoreface retreat model, a coastal lithosome which is experiencing a landward translation of the shoreface provides the primary source of sand to the shelf. During storm activity, geostrophic currents result in transportation of sediments into deeper water. Huthnance (1982) proposed a model in which a sand body could develop on the shelf in response to the seaward directed flows. Modern examples of features which formed as a result of the erosional shoreface retreat mechanism include the sand ridge complexes on the New Jersey shelf (Swift and Field, 1981; Rine et al, 1986; and Figueiredo et al, 1981). Ancient examples of shelf sandbodies which formed by this mechanism include the Tocito Lentil (Coniacian) (Kofron, 1987); the Semilla sandstone (Turonian) (LaFon,1981); the Shannon sandstone (Tillman and Martinsen, 1984); and the Duffy Mountain sandstone (Boyles et al, 1981). These features may form during a transgression (Tocito Lentil) which results in the formation of

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In at least three of the ancient examples (Tocito Lentil, Duffy Mountain, and Shannon), the sandstone body is assymetric with the steepest face occurring on the seaward side.

In the second mechanism (shelf plumes) of this category. Palmer and Scott (1984) suggest that aiong-shelf currents are directed seaward adjacent to distributary mouths. Diversion of the currents transports sediments beyond wave base and leads to the formation of a plume-shaped deposit. Patterson (1983) and Thompson et al (1986) have recognized shelf plumes in ancient sequences and cite the Nile delta complex as a modern analogue. Like the shelf sandridge model, large scale sandwaves with crests oriented transverse to the crest of the shoal are a common lithofacies of the shelf plume. Bioturbated shelf muds overly and underly the sandstone.

It is clear from these facies models that shoals which formed by transport of material into deeper water are predominantly characterized by the presence of physical sedimentary structures. These structures include large scale sandwaves, megaripple and wave ripple laminations. These structures may be very easily recognized in core and, therefore, there should be no difficulty in differentiating these features from a truncated shoreface. Submerged barrier islands are characterized by preservation of at least some component of the upper shoreface and beach facies. The transgressed- submerged shoal model (Penland and Boyd, 1985) may appear to have similar sedimentological attributes to the truncated shoreface. Both features are overlain by shelf muds and are extensively bioturbated. However, three important differences exist. First, the transgressed-submerged shelf shoal has a low preservation potential. These shoals ultimately degrade to the point that

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Secondly, if the shoal is preserved, the profile is characteristically assymetric toward shore (Penland and Suter, 1986). The truncated shoreface (as shown by Fig. 3.7) is assymetrical offshore. Thirdly, this type of shelf shoal is a transgressive feature. Unlike the truncated shoreface which overlies shelf muds, the transgressed-submerged shoal dlsconformably overlies interdistributary bay muds.

CONCLUSIONS

1. A large strike-oriented sandstone body that occurs in a stable region of an ancient sheif-margin was formed as a regressive beach ridge plain during a falling sea-level.

2. The regressive shoreface which formed under a falling sea-level as opposed to the more frequently cited rising sea-level model is characterized by a sharp basal contact with the underlying shelf mudstone. Also the degree of amalgamation of storm beds is minimal when regression occurs during a sea-level fall.

3. Syndepositional normal faulting occurred during the depositional sequence in which the regressive shoreface formed. However, the faulting did not create detectable thickening of the shoreface sandstones on the downthrown block. Some local thickening of mudstones across the fault planes was observed.

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4. The truncated progradational shoreface sequence may appear similar to some shelf shoals in the subsurface; however, the former may be characterized by an offshore assymetric profile; a conformable contact which overiies shelf mudstones; and a subtle increase in tempestites within the underlying mudstone.

REFERENCES

Aigner, T., 1985, Storm Depositional Systems: Dynamic Stratigraphy in Modern and Ancient Shallow-Marine Sequences, Springer-Verlag, Berlin, 174 p. Anisgard, H. W., 1970, Causes of dominantly arenaceous foraminiferal assemblages in downdip Wilcox of Louisiana: Gulf Coast Assoc. Geol. Soc. Trans., v. 20, p. 210-217. Bernard, H. A., Major, 0. F., and Parrot, B. S., 1959, The Galveston Barrier Island and environs - a model for predicting reservoir occurrence and trend: Gulf Coast Assoc. Geol. Soc. Trans., v. 9, p. 221-224. Bernard, H. A., LeBlanc, R. J., and Major, 0, P., 1962, Recent and Pleistocene Geology of Southeast Texas and Guidebook of Excursion: in Geology of the Gulf Coast and Central Texas and Guidebook of Excursions, Houston Geol. Soc., Houston, Texas, p. 175-224. Boyles, J. M., Kauffman, E. G., Kiteley, L. W., and Scott, A. J., 1981, Depositional Systems Upper Cretaceous Mancos Shale and Mesaverde Group, Northwestern Colorado -Fall Field Trip Guidebook, Rocky Mountain Section Soc. Econ. Paleontologists and Mineralogists Part 1, 81 p.

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Carter, G. H., 1978, A regressive barrier and barrier-protected deposit: Depositional environment and geographic setting of the Late Tertiary Cohansey Sand: Jour. Sed. Petrology, v. 48, p. 933-950. Curray, J. R., Emmel, F. J., and Crampton, P. J. S., 1969, Holocene history of a strand plain, lagoonal coast, Nayarit, Mexico; in A. A. Castanares and F. B. Phleger, eds.. Coastal Lagoons, A Symposium, Universidad Nacional Autonoma, Mexico, p. 63-100. Davidson-Arnott, R. G. D. and Greenwood, S., 1976, Facies relationships in a barred coast, Kouchibouguac Bay, New Brunswick, Canada: in R. A. Davis and R. L. Ethington, eds.. Beach and Nearshore Sedimentation, Soc. Econ. Paleontologists Mineralogists Spec. Pub. 24, p. 149-168. Demarest, J. M., Biggs, R. B., and Kraft, J. C., 1981, Time-stratigraphic aspects of a formation; Interpretation of surf ici al Pleistocene deposits by analogy with Holocene paralic deposits, southeastern Delaware: Geology, v. 9, p. 360-365. Edwards, M. B., 1980, The Live Oak delta complex - an unstable shelf-edge delta in the deep Wilcox trend of south Texas: Gulf Coast Assoc. Geol. Soc. Trans., v. 30, p. 71-79.

Edwards, M. B., 1981, Upper Wilcox Rosita delta system of south Texas: Growth-faulted shelf-edge deltas: Am. Assoc. Petroleum Geologists Bull.,

V. 65, p. 54-73. Elliot, T., 1978, Clastic shorelines: in R. G. Reading, ed.. Sedimentary Environments and Facies, Elsevier, New York, p. 143-177.

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Figueiredo, A. G., Swift, D. J. P., Stubblefield, W. L, and Clark, T. L , 1981, Sand

ridges on the inner Atlantic Shelf of North America: Morphometric comparisons with the Huthnance stability model: Geo-Marine Letters, v. 1, p. 187-191. Fischer, A. G., 1951, Stratigraphie record of transgressing seas in light of sedimentation on the Atlantic coast of New Jersey: Am. Assoc. Petroleum Geologists Bull., v. 45, p. 1656-1666.

Frazier, D. E., 1974, Depositional-episodes: Their relationships to the Quaternary stratigraphie framework in the northwestern portion of the Gulf Coast Basin: Geological Circular, 74-1, Texas Bureau Economic Geology, Univ. Texas, Austin, Texas, 28 p. Galloway, W. E. and Hobday, D. K., 1983, Terrigenous Clastic Depositional Systems, Springer-Verlag, New York, 423 p.

He ward, A. P., 1981, A review of wave-dominated clastic shoreline deposits: Earth Sci. Rev., v. 17, p. 223-276. Howard, J. D. and Frey, R. W., 1985, Physical and biogenic aspects of backbarrier sedimentary sequences, Coast, U.S.A.: Marine

Geol., V. 63, p. 77-127. Howe, H. V., 1962, Subsurface geology of St. Helena, Tangipahoa, Washington, and St. Tammany Parishes, Louisiana: Gulf Coast Assoc. Geol. Soc. Trans., v. 12, p. 121-155.

Hoyt, J. H. and Henry, V. J., 1967, Influence of island migration on barrier island sedimentation: Geol. Soc. America Bull., v. 78, p. 77-86. Huthnance, J. M., 1982, On one mechanism forming linear sand banks: Estuarine, Coastal and Shelf Sci., v. 14, p. 79-99.

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Johnson, D. W., 1919, Shore Processes and Shoreline Development, John Wiley, New York, 584 p.

Kofron, B., 1987, Facies characteristics of the upper Cretaceous Tocito sandstone, San Juan Basin, New Mexico; Baton Rouge, Louisiana State University, Master's thesis.

Kraft, J. 0., 1971, Sedimentary facies patterns and geologic history of a

Holocene marine transgression: Geol. Soc. America Bull., v. 82, p. 2131- 2158. Kraft, J. O., Biggs, R., and Halsey, S. D., 1973, Morphology and vertical sedimentary sequence models in Holocene transgressive barrier systems: in D. R. Coates, ed.. Coastal Geomorphology, Proc. 3rd Am. Geomorph. Symp. Series, p. 321-354. Kraft, J. C. and John, C. J., 1979, Lateral and vertical facies relations of a transgressive barrier: Am. Assoc. Petroleum Geologists Bull., v. 63, p. 2145-2163.

LaFon, N. A., 1981, Offshore bar deposits of Semilla Sandstone Member of Mancos Shale (Upper Cretaceous), San Juan Basin, New Mexico: Am. Assoc. Petroleum Geologists Bull., v. 65, p. 706-721. Lowry, P., Nummedal, D., and Reimnitz, E., 1985, Development of inner shelf shoals on the Alaskan Beaufort Sea Shelf (abs.): Geol. Soc. Amer. Conference, Orlando, Florida.

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McCubbin, D. G., 1982, Barrier island and strand-plain facies: in P. A. Scholle and D. R. Spearing, eds.. Sandstone Depositional Environments, Am. Assoc. Petroleum Geologists Memoir 31, p. 247-280. Miall, A. D, 1984, Principles of Sedimentary Basin Analysis, Springer-Verlag, New York, 490 p. Palmer, J. J. and Scott, A. J., 1984, Stacked shoreline and shelf sandstone of LaVentana Tongue (Campanian), northwestern New Mexico: Am. Assoc. Petroleum Geologists Bull., v. 68, p. 74-91. Patterson, J. E., 1983, Exploration potential and variations in shelf plume sandstones, Navarro Group (Maestrichtian), east central Texas: Austin, Univ. Texas, Master's thesis, 91 p. Penland, S. and Boyd, R., 1985, Transgressive Depositional Environments of the Mississippi River Delta Plain: A Guide to tne Barrier Islands. Beaches and Shoals in Louisiana: Louisiana Geological Survey Guidebook Series No. 3, Baton Rouge, Louisiana, 233 p. Penland, S. and Suter, J. R., 1986, Criteria for distinguishing submerged barrier

islands and inner shelf shoals. Northern Gulf of Mexico (abs.): Soc. Econ. Paleontologists Mineralogists Annual Midyear Meeting, Raleigh, , p. 88. Psuty, N. P., 1966, The geomorphology of beach ridges in Tabasco, Mexico, Technical Report 30, Coastal Studies Institute, Louisiana State University, Baton Rouge, Louisiana, 51 p. Reineck, H. E. and Singh, I. B., 1971, Der Golf von Gaeta/ Tyrrhenisches Meer. 3. Die Gefuge von Vorstrand-und Sehelfsedimenten: Senckenbergiana marit, 3, p. 185-201.

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Reineck, H. E. and Singh, 1. B., 1980, Depositional Sedimentary Environments - With Reference to Terrigenous Clastics, 2nd ed., Springer-Verlag, New York, 549 p. Reinson, G. E., 1984, Barrier island and associated strand-plain systems: in R. G. Walker, ed.. Facies Models, 2nd ed., Geosci. Can. Reprint Series 1, p. 119-140. Rine, J. M., Tillman, R. W., Stubblefield, W. L , and Swift, D. J. P., 1986, Lithostratigraphy of Holocene sand ridges from the nearshore and middle continental shelf of New Jersey, U. S. A.: InT. F. Moslow and E. G. Rhodes, eds.. Modern and Ancient Shelf Clastics: A Core Workshop, Soc. Econ. Paleontologists Mineralogists Core Workshop No. 9, p. 1-72. Roep, T. B., Beets, D. J., Dronkert, H., and Pagnier, H., 1979, A prograding coastal sequence of wave-built structures of Messinian age, Sorbas, Almeria, Spain: Sedimentary Geol., v. 22, p. 135-169. Sanders, J. E. and Kumar, N., 1975, Evidence of shoreface retreat and in-place 'drowning' during Holocene submergence of barriers, shelf off Fire Island, New York: Geol. Soc. America Bull., v. 86, p. 65-76. Self, G. A., Breard, S. Q., Rael, H. P., Stein, J. A., Thayer, P. A., Traugott, M. O., and Easom, W. D., 1986, Lockhart Crossing field: New Wilcox trend in southeastern Louisiana: Am. Assoc. Petroleum Geologists Bull., v. 70, p. 501-514. Suter, J. R. and Berryhill, H. L., Jr., 1985, Late Quaternary sheif-margin deltas, northwest Gulf of Mexico: Am. Assoc. Petroleum Geologists Bull., v. 69, p. 77-91.

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Swift, D. J. P. and Field, M. E., 1981, Evolution of a classic sand ridge field: sector. North American inner shelf: Sedimentology, v. 28, p. 461-481. Tavener-Smith, R., 1982, Prograding coastal facies associations in the Vryheid Formation (Permian) at Effingham Quarries near Durban, South Africa: Sedimentary Geol., v. 32, p. 111-140. Thompson, S. L , Ossian, C. R., and Scott, A. J., 1986, Lithofacies, inferred processes, and log response characteristics of shelf and shoreface sandstones. Perron Sandstone, Central Utah: in I. F. Moslow and E. G. Rhodes, eds.. Modern and Ancient Shelf Clastics: A Core Workshop, Soc. Econ. Paleontologists Mineralogists Core Workshop No. 9, p. 325- 361. Tillman, R. W. and Martinsen, R. S., 1984, The Shannon shelf-ridge sandstone complex, Salt Creek anticline area, Powder River basin, Wyoming: in R. W. Tillman and C. T. Siemers, eds., Siliciclastic shelf sedimentation, Soc. Econ. Paleontologists Mineralogists Spec. Pub. 34, p. 85-142. Tye, R. S., Ranganathan, V., and Ebanks, W. J., 1986, Facies analysis and reservoir zonation of a Cretaceous shelf sand ridge: Hartzog Draw field, Wyoming: in T. F. Moslow and E. G. Rhodes, eds.. Modern and Ancient Shelf Clastics: A Core Workshop, Soc. Econ. Paleontologists Mineralogists Core Workshop No. 9, p.169-216.

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Winker, C. D., 1982, Cenozoic shelf margins, northwestern Gulf of Mexico Basin: Gulf Coast Assoc. Geol. Soc. Trans., v. 32, p. 427-448. Winker, C. D., 1984, Clastic shelf margins of the post-Commanchean Gulf of Mexico: Implications for deep-water sedimentation: Gulf Coast Section Soc. Paleontologists Mineralogists Foundation Research Conference, Austin, Texas, p. 282-293.

Winker, C. D. and Edwards, M. S., 1983, Unstable progradational clastic shelf margins: in D. J. Stanley and G. T. Moore, eds.. The Shelfbreak - Critical interface on Continental Margins, Soc. Econ. Paleontologists Mineralogists Spec. Pub. 33, p. 139-157.

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NUMERICAL SIMULATION OF STRATIGRAPHIC SEQUENCES AND SHOREFACE SEQUENCES FROM A CLASTIC SHELF-MARGIN

ABSTRACT

Two computer programs were developed to simulate clastic depositional sequences on an ancient passive continental sheif-margin setting at two contrasting stratigraphie levels. The first program (STRATSIM) is based on Pitman's (1978) model which defines the relationship between eustacy and stratigraphie sequences. STRATSIM examines the influence of sea-level change and basin subsidence on the generation of depositional sequences which occur on the Wilcox (Paleocene-Eocene) sheif-margin of central Louisiana. These sequences may be considered age equivalents of third or lower (glacial) global sea-level cycles. Using published values for the wavelength and amplitude of global sea-level fluctuations (Vail et al, 1977), the

program defines the shelf profile and calculates the position of the shoreline after each time step. Computed sequence boundaries and shoreline shifts based on third-order and glacial-type global sea-level fluctuations did not correspond with those observed from the Wilcox sheif-margin. Rather, minor

changes in the rate of eustatic sea-level fall over a relatively short time span (5x105 to 1Q6 years) generated a pattern which was more representative of the observed offlapping pattern and shoreline shifts.

183

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Program DEPSIM examines depositional sequences at the level of a single depositional event. The program was designed to simulate the resultant facies sequences of a progradational shoreface under variable conditions of sea-level, sediment supply and subsidence. The purpose of these simulations is to explain observed differences in transition zone facies between two relatively similar shoreface sequences from the Wilcox sheif-margin trend. The program is a biased random-walk model which simulates sea-level change, sediment switching, deposition of tempestites within the transition zone, and regional and localized subsidence. Results of the program show that a prograding shoreface which forms under a falling relative sea-level experiences a greater basinward translation of transition zone facies than one formed under a rising sea-ievel. Consequently, a vertical profile through a shoreface which formed during a relative sea-level fall would show a decrease in the frequency and thickness of tempestites in comparison to a shoreface which formed during a relative sea-level rise. The net result of the decrease in occurrence and reduction in thickness of tempestites is the appearance of a sharp basal contact between the transition zone and shoreface facies. Further refinement of these programs will enable the prediction of regional sequence stratigraphy and the facies architecture of component shallow marine depositional events.

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INTRODUCTION

The objective of many stratigraphie and sedimentoiogic basin studies is the development of depositional models and paleogeographic reconstructions. These models often contain inferences regarding changes in sea-level, sediment supply, or basin tectonism as a means of explaining the variability of sedimentary facies and arrangement of depositional sequences. However, in many instances these depositional models are not tested and are, therefore, speculations. Numerical simulation of geologic processes provides a means to test stratigraphie concepts which are intrinsic to these depositional models. In this chapter, two fundamental stratigraphie concepts are evaluated using computer simulation techniques. The first of these concepts concerns the influence of sea-level change on the development of depositional sequences which occur on an ancient sheif- margin (See Chapter 1). This model implies that global sea-level would periodically rise and fail by magnitudes determined by the addition of individual cycle amplitudes. Published values are given for the amplitude and wavelength of these sea-level cycles (Nummedal, 1983). According to Vail et ai (1977) and Haq et al (1987), the Phanerozoic sea-level curve can be viewed as a summation of several orders of these discrete sea-level cycles. Pitman (1978) and Pitman and Golovchenko (1983), however, propose that eustatic sea-level does not experience such cyclic fluctuations in the absence of glacially-induced changes, but rather shows minor changes in the long term rate of sea-level rise or fall. The stratigraphie sequences which develop according to this model are a result of the interaction of changes in the

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rate of global sea-level rise or fall and basin subsidence. A computer program (STRATSIM) was written to determine whether the depositional sequences observed on the Wilcox sheif-margin were a response to global sea-level cycles (Vail et al, 1977) or to changes in the rate of Cenozoic eustatic sea-level fall (Pitman, 1978).

The second concept concerns the facies architecture of a single depositional event from the Wilcox sheif-margin. Observations of two progradational shoreface sequences from separate regions of the sheif-margin revealed that significant sedimentoiogic differences exist in the transition zone facies of each sequence. The transition zone facies of one of these shoreface sequences (Fordoche field; Chapter 2) is typical of modern examples of beach to shelf profiles (Bernard et al, 1962; Reineck and Singh, 1971; Reineck and Singh, 1980; Aigner, 1985; Howard and Reineck, 1972; Howard and Reineck, 1981).

The transition zone facies of modern beach to shelf profiles exhibit the following characteristics; a) an upward increase in thickness and frequency of individual storm layers (tempestites); b) amalgamation of tempestites near the upper contact with the main shoreface sands; and c) a high degree and upward increase in burrowing of transition zone muds. In the second shoreface sequence (Lockhart Crossing; Chapter 3), the transition zone facies does not exhibit the amalgamation of tempestites or high degree of burrowing that is characteristic of the first prograding shoreface.

While the variation in transition zone facies between these two sequences may be due to differences in climate (i.e. frequency and magnitude of storms) which occurred during their formation, it is also possible that they are due to

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deposition which occurred under different conditions of sea-level change. Heward (1981) and Reinson (1984) suggested that a prograding shoreface sequence which formed under a falling sea-level would exhibit a sharp basal contact between the transition zone and shoreface facies. Therefore, the appearance of this shoreface sequence differs from the more commonly encountered shoreface which has a gradational basal contact. In order to test this model, a computer program (DEPSIM) was developed to examine how the facies architecture of a prograding shoreface that formed during a falling sea- level would differ from one that formed during a rising sea-level.

The development and further refinement of these computer programs (STRATSIM and DEPSIM) can provide valuable insight into complex geologic interactions. Both these programs examine basin subsidence, shoreline shifts, and sea-level change; however, STRATSIM simulates these processes over geologic time (>105 years) whereas DEPSIM simulates them over a much

shorter time period (100 to 104 years). Therefore, these programs provide the basis of a numerical model which will facilitate the prediction of facies sequences at both a regional and local scale.

This chapter is arranged in two sections. The first section deals with the simulation of depositional sequences on the Wilcox sheif-margin. The second section examines the simulation of prograding shoreface sequences. In both sections, an outline of the program structure is described followed by the presentation of results of the simulation experiments.

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SIMULATION MODEL FOR STRATIGRAPHIC SEQUENCES

Introouction

This section presents the theory and results of a computer program written by this author to simulate the formation of depositional sequences on a passive continental margin. The fundamental structure of the program is based on algorithms presented by Pitman (1978). In his paper, Pitman demonstrated how relatively minor variations in two geologic processes, eustatic sea-level and basin subsidence, could account for major Tertiary transgressions and regressions (Fig. 4.1). In Pitman's model, basin subsidence remained constant (2.5 cm 1Q3 years'i at the shelf-edge) throughout the development of individual sequences. Eustatic sea level, however, dropped from the late Cretaceous highstand and exhibited several changes in the rate of fall (Fig. 4.2). These variations in the rate of sea-level fall, according to Pitman, reflect changes in the ocean volume and are initiated by changes in the spreading rate of mid- oceanic ridges. Although relatively subtle, these variations in the rate of sea- level change relative to basin subsidence were sufficient to generate regional transgressive and regressive events. Pitman's model was operative over a relatively long time interval (each

sequence represented 10^ years). This author has attempted to apply Pitman's approach on a much finer scale (i.e. 10^ to 10® years) to account for the occurrence of depositional sequences observed on the Wilcox sheif-margin. This scale would, in essence, simulate the development of third and fourth- order depositional sequences (1Q4 tolO^ years).

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Figure 4.1 Calculated shoreline positions from the Upper Cretaceous through Miocene based on Pitman’s data for global sea-level fall. (See Fig.4.2). (After Pitman, 1978).

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Figure 4.2 Global sea-level curve, upper Cretaceous through Miocene, based on spreading rates of mid-oceanic ridge system. The stippled area depicts the approximate time interval of Wilcox deposition. (Modified after Pitman, 1978).

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Wilcox depositional sequences

Lowry (Chapter 1) has shown that at least seven major depositional sequences occur within the stable sheif-margin region of the Wilcox Group in Louisiana (Fig. 4.3). These sequences are bounded by laterally continuous thick shale intervals (15 to 25 m thick) which may extend up to 100 km landward from the previous maximum basinward position of the shoreline. Downdip, these shale intervals merge with basinal mudstones. The shale intervals may also be traced over 200 km to the west along depositional strike. Although the time interval of the individual sequences is unknown, it is likely that they range in age from 10^ to 10^ years (Lowry, Chapter 1). Therefore, these sequences are similar to third or fourth-order sequences (Vail et al, 1977; Miall, 1984) and depositional episodes (Frazier, 1974). There are three possible explanations to account for the occurrence of these sequences within the Wilcox sheif-margin. These explanations are: a) autocyclicity of sediment supply occurring concomitantly with relative rising sea-level; b) fluctuations in the rate of eustatic sea-level fall; and c) low order eustatic sea-level cycles.

There are insufficient data to establish whether or not sediment supply was periodically fluctuating (i.e. sediment switching on the order of every 105 to 106 years) on a basinwide scale throughout the duration of Wilcox deposition. Therefore, this explanation must remain as a possibility to account for the development of the sequences. Hence, this section will only examine the last two explanations as probable causes for the development of the sequences. A

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series of experiments were performed to determine the most likely explanation for the development of stratigraphie sequences on the Wilcox sheif-margin. These experiments were conducted using a computer program (STRATSIM) to model stratigraphie sequences.

STRATSIM: program structure

Program STRATSIM begins by computing an initial continental shelf profile through the use of simple trigonometry. Shelf length and slope are specified as input (constant length 250 km, constant slope 0.1°). Depths are computed at 10 km intervals along the profile.

Sea-level data may be entered in two modes. The first of these modes uses Pitman's data (1978) which consists of a linear rate of sea-level fall for each time step (see Fig. 4.2). The second mode of sea-level data entry is based on global sea-level cycles (Vail et al, 1977). These global cycles have specific amplitudes and frequencies (Nummedal, 1983) (Table 4.1). The user may choose to incorporate a single sea-level cycle or any combination of up to four cycles. The program can be initialized to begin the simulation from any point on the sea-level cycle. For example, the simulation can begin from either a sea-level highstand or a sea-level lowstand. After the user specifies the method of sea-level computation, the program calculates two fundamental variables for each iteration. These variables are: 1) net deposition or erosion at every point along the shelf profile, and 2) the new location of the shoreline for each time step. Theses variables are computed using equations (1) and (2), respectively.

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CYCLE RANGE IN SEA-LEVEL (M) TIME INTERVAL (YRS.) RATE (CM/YR) EXAMPLE

1st Order 500 200000000-300000000 0 .0 0 0 2 5 Early Jurassic to Late Cretaceous 2nd Order (Supercycles) 2 0 0 10000000-80000000 0.002-0.00025 Throughout the Phanerozoic 3rd Order (Global cycles) 200 1000000-10000000 0 .0 2 -0 .0 0 2 Mesozoic and Cenozoic cycles Glacial 100 100 0 0 0 0 0 .0 2 Nebraskan Glaciation Glacial 100 2 0 0 0 0 0 0 .0 5 lllinolslan substages Glacial 100 2 0 0 0 0 0 .5 -1 AltoNan or Woodfordian-Holocene Holocene 2 .5 300 0.8 Dunkirk 0 transgression Holocene 1.2 4 0 0 0.3 Uttle Ice Age - present Recent (last 100 years) 0 .1 2 100 0 .1 2 Recent tide gage records Multi-year cycles 0 .0 5 5 - 1 0 0 .5 -1 Recent tide gage records

Table 4.1 Summary of various types of sea-ievel fluctuations and their durations and amplitudes. (Modified after Nummedal, 1983).

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TR XR ss DS| ^li ^ss Sed = T - RsiT- Rgl + 8 - DS| Equ. 1 'ss D

TR _D_ D D D8| D + 8 - - 0 Rsi + 8 - - X|i Equ. 2 Rss 'ss 'ss 'ss

Where, X = Any location on the shelf. X| = Location of shoreline after time J X|j = Initial location of the shoreline during time J. D = Distance from hinge line to shelf-edge. Rgl = Rate of sea-level change Rgg = Rate of tectonic subsidence at the shelf-edge. 8 = Uniform sedimentation rate. T = Time interval. 8| = Slope of continental shelf.

In Pitman's model, the shelf profile exhibits maximum subsidence at the shelf-edge, diminishing to zero toward the hingeline. STRATSIM also simulates a maximum subsidence at the shelf edge; however, there is an additional option to model uniform subsidence along the entire profile. After each depositional value has been computed along the shelf profile, the new shelf profile is defined. As each new profile is computed, the underlying strata are subsided at a rate determined by their position on the shelf profile. Since the program does not simulate lithology within each sequence no attempts were made to account for sediment compaction within each sequence.

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In order to calibrate the program STRATSIM, the simulations performed by Pitman were replicated using his original data. Figure 4.4 compares the sequences presented in Pitman's paper with those calculated by STRATSIM. Figure 4.5 shows a correlation of the shoreline locations computed by STRATSIM and those presented by Pitman (1978).

Modeling the Tertiary sequence using hiqh-order global sea-level cycles

A series of tests (see Table 4.2) were performed using the global sea- level cycle data to examine whether a combination of first and second-order sea-level cycles could produce the Tertiary sequence described above.' Accurate modeling of the sequence using these data would provide a basis on which to compute a value of high order sea-level change for the period of Wilcox deposition.

In preliminary runs of the program, a first-order cycle was used to approximate the general falling sea-level trend from the end of the Cretaceous highstand. Figure 4.6 shows the computed sequence boundaries, shoreline shifts and sea-level cun/es for a range of first-order cycles. In figures 4.6a, 4.6b and 4.6c, the amplitude was held constant (250 m) and the wavelength of the cycle was varied. Figure 4.6a shows the predicted sequence stratigraphy for a first-order cycle with a wavelength of 15 x 107 years. In this simulation a period of offlap (75 to 45 ma) is followed by a period of gradual onlap (45 to 25) before a major onlapping event occurred between 25 and 15 ma. Increasing the wavelength of the the cycle (Figs. 4.6b and 4.6c) results in a reduction of the magnitude of onlap between 25 and 15 ma. Figures 4.6d and 4.6e show the

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& I [ 65 to 45 m a ] Q [ 85 to 15 m a ] lie

01 mm SI

3 0 K * I I

. Sl > 4 » a

7 0 km H I

Figure 4.4 Comparison of computed Tertiary sequence boundaries presented by Pitman (1978) (d-g) with those computed by STRATSIM (a-c). Note the differences in horizontal and vertical scales.

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100

I 90 Y=0.985X-0.144

® 80 Ë S 70. .<2 9 , 60. 03 ■_ 50.

§ 40. cc 5 30. 20

0 3

0 10 20 30 40 50 60 70 80 90 100 PITMANS RESULTS (Distance in km)

Figure 4.5 Linear regression of computed shoreline positions from the sequences shown in Figure 4.4 (d-g) with those in Figure 4.4 (a-c).

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FIGURE WAVELENGTH 1 AMPLITUDE 1 WAVELENGTH 2 AMPLITUDE2 WAVELENGTH 3 AMPLITUDE 3 (YEARS) (M) (YEARS) (M) (YEARS) (M) Fig. 6a 150,000,000 250 Rg. 6b 200,000,000 250 Fig. 6c 250,000,000 250 Rg. 6d 250,000,000 275 Rg. Be 250,000,000 200

Rg. 7a 250,000,000 275 100,000,000 100 Rg. 7b 250,000,000 275 10,000,000 100 Rg.7c 250,000,000 275 50,000,000 100 Fig. 7d 250,000,000 275 50.000.000 25

Fig. 8a 250,000,000 275 50,000,000 25 10,000,000 100 Rg. 8b 250,000,000 275 50,000,000 25 5,000,000 100 Fig. 8c 250,000,000 275 50,000,000 25 1,000,000 100

Rg. 9a 250,000,000 275 50,000,000 25 1,000,000 50 Fig. 9b 250,000,000 275 50,000,000 25 1,000,000 25 Fig. 9c 250,000,000 275 50,000.000 25 1,000,000 10 Fig. 9d 250,000,000 275 50,000,000 25 1,000,000 5

Table 4.2 List of simulations performecj by program STRATSIM.

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Figure 4.6 Sequence boundaries, sea-level curves, and shoreline shifts for the computed Tertiary sequences using program STRATSIM and assuming first-order global sea-level cycles. a) 150 million years wavelength; 250 m amplitude b) 200 million years wavelength; 250 m amplitude c) 250 million years wavelength; 250 m amplitude d) 250 million years wavelength; 200 m amplitude e) 250 million years wavelength; 275 m amplitude

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O iitv c * from hingttirw (km) SO 100 ISO 200 250 0

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sequence boundaries which were computed using a constant wavelength of 250 ma and amplitude values of 200 and 275 m respectively. Increasing the amplitude of the sea-level cycle in this case results in a reduction in the magnitude of the transgression which occurs between 25 and 15 ma. In terms of a first-order approximation to the Tertiary sequence boundaries, figure 4.6e (which depicts a sea-level cycle a wavelength and amplitude of 250 ma and 275 m respectively) appears to yield the closest resemblance to the generalized stratigraphy. The above wavelength and amplitude values were used as input for the subsequent tests in which an additional lower order (2nd) sea-level cycle was added to the first-order curve. Table 4.2 shows the range of wavelength and' amplitude values used for the simulation of sequences which formed in response to the second-order sea-level cycles. The first two simulations represent the maximum and minimum values for the second-order sea-level cycles (wavelengths of 100 ma and 10 ma, with an amplitude of 100m). With a wavelength of 100 ma (Fig. 4.7a), the computed sequences showed a period of initial offlap, followed by a major transgressive period. At the other end of the scale (10 ma wavelength), the program predicted a progressively offlapping sequence (Fig. 4.7b). Using an intermediate wavelength value of 50 ma, the program predicted a major transgression occurring in the late Eocene followed by another during Miocene time (Fig. 4.7c) as did Pitman’s model. However, the magnitude of the shoreline migration in response to the transgressions is at least one order of magnitude greater than that predicted by Pitman's data (see Fig 4.1). After a series of tests which varied the amplitude and the wavelength of the second-

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Figure 4.7 Computed Tertiary sequence boundaries and shoreline shifts using a first-order global sea-level cycle with a 250 million years wavelength and 275 m amplitude and variable second-order cycles. a) Second-order cycle: 100 million years wavelength - 100 m amplitude b) Second-order cycle: 10 million years wavelength - 100 m amplitude c) Second-order cycle: 50 million years wavelength - 100 m amplitude d) Second-order cycle: 50 million years wavelength - 25 m amplitude

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D iittn c * iroffl rwigatM in un

ISO 200 250 100 ma 100m

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OiiQnc* from nnganw m un 10 m a ISO 200 250 100m 20

I I I I £ 6 0

8 0

Distança of shorallna from hInQollna (km)

Otiune* koffl rtigtm * »i un 50 m a ISO 200 250 too m I 20 I I £

6 0 I

Distança of shoreiins from hingailna (km) DUanoo torn Mnpmm n km

SO 250

SO m a

20

Ê £ too 4 0 I 6 0

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order cycle, the combined first and second-order global sea-level cycles which produced the closest approximation to Pitman's results were determined (Fig. 4.7d). The resultant sea-level curve is composed of the first-order sea-level cycle described above and a second-order sea-level cycle with a wavelength of 50 ma and an amplitude of 25 m. Again, these values for the sea-level cycles are considerably different from the data presented by Vail et al (1977).

Simulation of Wilcox depositional sequences Introduction

The two sea-level cycles described above and the sea-level curve presented by Pitman were used to determine high order sea-level fall during the period of Wilcox deposition. Pitman’s data predicted a constant sea-level decline of 0.62 to 0.65 cm 10'3 years. A sea-level fall of 0.533 cm 10^ years was predicted by combining the first and second-order sea-level cycles. This general rate of sea-level fall was added to the low order glacial cycles in order to produce a more realistic sea-level curve.

Two basic experiments were undertaken in order to simulate the development of sequences on the Wilcox shelf-margin. The first experiment examines the stratigraphie sequences which would result from a cyclical sea- level curve. Using the wavelength and amplitude data outlined by Nummedal (1983) for third-order and glacial sea-level cycles, it was possible to simulate the development of sequences which would form in response to these sea- level fluctuations.

The second experiment simulates the development of sequences which formed during a falling sea-level exhibiting unequal rates of decline. Since

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there are no data available for changes in eustatic sea-level fall on the scale examined here (5x105 to 10® years), a range of hypothetical rates of sea-level change are used. These data demonstrate the effect of this type of sea-level curve on the development of stratigraphie sequences.

Sequences resulting from third-order and alacial-tvoe global sea-level cycles

a) constant sea-level amplitude and variable wavelength

Figure 4.8 shows the stratigraphie sequences which would result if a third-order sea-level cycle was superimposed on the combined first and second-order curve defined in the previous section. At the maximum limit of sea-level cycle wavelength (10? years), there is an initial seaward progradation (offlap) followed by a major onlapping event as the shoreline is

translated 6x102 km landward (Fig. 4.8a). Two offlapping events separated by a major transgression are predicted by STRATSIM when a wavelength of 5 ma is used (Fig. 4.8b). The predicted shoreline translation approaches 103 km. Reducing the wavelength in this case to 106 years (Fig. 4.8c) generates at least six Wilcox sequences within the stable portion of the margin but still results in a general onlap. The computed sequence stratigraphy shows little resemblance to the Wilcox sequences. Figure 4.8c shows the resultant sequence stratigraphy for an intermediate wavelength value of 5x 10® years.

b) constant wavelength and variable amplitude It is apparent from the simulations described above that a third-order or glacial sea-level fluctuation should have a wavelength on the order of 10® years in order to account for the occurrence of sequences within the Wilcox

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Figure 4.8 Computed Wilcox sequence boundaries and shoreline shifts using a combination of first, second (see Fig. 4.7d), and third-order global sea-level cycles. a) Third-order cycle: 10 million years wavelength -100 m amplitude b) Third-order cycle: 5 million years wavelength -100 m amplitude c) Third-order cycle: 1 million year wavelength -100 m amplitude

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Distance from hingeline (km)

50 100 150 250 10 ma 50 100 m

52 I E I 5u i 54 I 56 58 200

Distance of shoreline from hingeilne (km)

50 5 Ma 100 m

g I

58

Distança ol shoreline front hingeilne (km)

50

52 i I 54 56 1 Ma 58 100 m

Distance of shoreline from hingeline (km)

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shelf-margin. Consequently, another series of experiments were conducted to examine the effects of varying the amplitude of the sea-level fluctuation while holding the wavelength constant at 10® years. Figure 4.9a shows the predicted sequence stratigraphy and shoreline position for a sea-level cycle with an amplitude of 50 m. The range in shoreline migration exceeds 500 km and the overall trend depicts an onlapping

sequence. Reducing the amplitude to 25 m results in a decrease of shoreline migration to approximately 250 km (Fig. 4.9b). Figures 4.9c and 4.9d show that the resuiting shoreline translation can be reduced to a magnitude comparable to that observed on the Wilcox shelf-margin (30 to 100 km) when sea-level cycle amplitudes of 10 and 5 m are used as input to the program, in figure 4.9c a 10 m sea-level cycle amplitude results in little or no migration of the basinward extent of computed shoreline positions throughout the period of Wilcox deposition. A 5m amplitude (Fig. 4.9d) results in a general offlapping trend. These two simulations (Figs. 4.9c and 4.9d) represent the closest approximation to the Wilcox sequences.

Sequences resulting from variations in the rate of eustatic sea-level fall

It is apparent from the above simulations that the range of values for wavelength and amplitude of third and lower order sea-level cycles reported in the literature (Vail et al, 1977; Nummedal, 1983) cannot account for the occurrence of depositional sequences observed on the Wilcox shelf-margin. Consequently, the type of sea-level curve proposed by Pitman was used as input to the program in an attempt to determine if its interaction with basin

subsidence could generate those sequences observed on the Wilcox shelf- margin. Pitman has shown how fluctuations in the rate of eustatic sea-level fall

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Figure 4.9 Computed Wilcox sequence boundaries and shoreline shifts using a combination of first, second (see Fig. 4.7d) and third order global sea-level cycles. a) Third-order cycle; 1 million year wavelength - 50 m amplitude b) Third-order cycle: 1 million year wavelength - 25 m amplitude c) Third-order cycle: 1 million year wavelength -1 0 m amplitude d) Third-order cycle: 1 million year wavelength -5 m amplitude

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Distance from hingeline (km) a 0 50 100 150 200 250

Distance from hingeline (km) Distance of shoreline from hingeilne (km) •50 100 150 200 250

Distance from hingeline (km) Distance of shoreline from hingeline (km) 50 100 150 200 250 5 0 -

O ’ O

Distance from hingeilne (km) Distance of shoreline from hingeilne (km) 50 100 150 200 250 5 0 1 ma

Distance of shoreline from hingeline (km)

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could account for the occurrence of stratigraphie sequences on the order of 10? years, in the approach adopted here, a hypothetical stair-step failing sea-ievei curve (Fig. 4.10) was assumed to have occurred during deposition of the Wilcox.

Two basic assumptions regarding this sea-ievei curve were made in order to conform with the observed sequence stratigraphy of the Wilcox shelf-margin. First, at least seven major sequences must occur throughout the period of Wilcox deposition. Secondly, given the rate of first-order eustatic sea-ievei fail described above (0.533 to 0.65 cm 103 years’ ■•), the total sea level fail should be between 30 to 50 m throughout the duration of Wilcox deposition.

a) Stair-step sea-ievei fail - lOQ vear intervals Figure 4.11 shows the results of a series of simulations where the total fail

in sea-ievei was 50 m over 7 x106 years, in these simulations, subsidence decreased from a maximum at the sheif-edge to zero at the hingeline. Ail the simulations predict the general offlapping pattern and, except where the difference in the rate of change in sea-ievei fail is minimal (Fig. 4.1 Id), transgressive and regressive events can be simulated without a eustatic sea- ievei rise. The range in the magnitude of each transgression is similar to those observed in the Wilcox shelf-margin. However, fluctuations in sea-level on the

order of 106 years only result in the development of three major sequences.

b) Stair-step sea-level fall - 500.000 vear intervals

It is apparent from the previous section that fluctuations in the rate of sea-

level fall which occurred on the order of 106 years, could not be used to

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Figure 4.10 Hypothetical falling sea-level curves for the period of Wilcox deposition. SL=sea-level fall in cm per year a) SL1= 0.001 cm per year (1 cm/ lOOOyears) SL2= 0.0003 cm per year (0.3 cm/ lOOOyears) 106 year increments b) SL1 = 0.0005 cm per year (0.5 cm /10OOyears) SL2= 0.00065 cm per year (0.65 c m /10OOyears) 106 year increments c) SL1 = 0.0002 cm per year (0.2 cm /10OOyears)

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60 60 S U = 0.001 SL2=O.OOfi3 SL1 =0.001 SL2=0.0003 50 - SO 1 ma interval 500,000 year interval E 40

@ 3 0 - ■© > 30 ffl 20 @ co CO 10 - 10

0 ...... I ' I B.Oe+6 2 .08+6 0.08+0 8.08.6 6.08.6 4.08.6 2.08.6 0.0 8 .0 Time Time (yrs)

60 60 1 SL1 =0.0005 SL2=0.00065 SL1 =0.0005 SL2=0.00065 50 1 ma Interval 5 0 - 'e 4 0 -

I .. 1 é I B. CO 2 0 -

10 ■ 10- -S.O a.6 ■6.08.6 -4.08.6 -2.08.6 0.08.0 -8 .0 8.6 -6 .08 . 6-. -8 ,-2.08.6 0.08.0 Time (yrs) Time (yrs)

60 6 0 - SU =0.0002 SL2=0.0014 SL1 = 0,0002 SL2=0.0014 50 - . 1 ma interval 500,000 year Interval JE 4 0 -

30 f 3 0 - \ M ■ 20 V « 2 0 - © CO 10 - 1 0 -

0 - •6.08+6 '6.08+6 -4.08+6 -2.08+6 0 .0 8 .0 8.08.6 6.08.6 4.08.6 2.08.6 0.08+0 Time (yrs) Time (yrs)

60 60 ' su =0.0 SL2=0.0016 50 SL1=0.0 SL2=0.0016 5 0- 1 ma interval 500,000 year interval 40 E 40 -

S g 30 - 20 ta 2 0 - “ ...

*6.08+6 -6.08+6 *4.08+6 *2.08+6 0.08+0 - 8 .08+6 •6.08+6 -4.08+6 -2.08+6 0 .0 8 .0 Time (yrs) Time (yrs)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 215 Distance from Migelhe (km) 100 ISO 200 50 SL1-0.001 SL2-0.003 52 i 54 — 100 I

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200 58 Distance from Nngeline (km) Distance of shoreline from hingeline (km)

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Figure 4.11 Computed sequence boundaries and shoreline shifts assuming a variable rate of sea-level fall using the sea-level curves shown in Figure 4.10 a, b, c, and d.

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account for the number of sequences observed in the Wilcox margin. The time interval for changes in the rate of sea-level fall was reduced to 500,000 years and the experiments were repeated using the input data from the previous section. The results of these simulations are the closest approximation to the Wilcox sequences. Figure 4.12 shows that a sea-ievei fail that fluctuates between 0 and 1 cm per 10^ years would generate regional transgressions comparable in magnitude to those observed in the Wilcox.

Discussion

There are two important points regarding the Vail sea-level cycles that

may have a direct effect on the development of stratigraphie sequences. First,' there is little physical basis for suggesting that high order (first, second, and possibly third-order) sea-level cycles are periodic. It is evident that glacially- induced sea-level fluctuations (fourth-order) may exhibit a periodicity in response to astronomical (Milankovitch-type cycle) effects or negative- feedback associated with the development of polar landmasses (Ewing and Donn, 1958). However, there is little evidence to suggest the occurrence of Mesozoic or Cenozoic polar glaciations which are comparable in magnitude to those which developed after Miocene time (Pitman and Golovchenko, 1983). The second point about the Vail et al (1977) concept of global sea-level cycles concerns the origin of a mechanism other than glaciations, which could create large- scale fluctuations in sea-level over a relatively short time period. For example, in some cases, eustatic sea-level is believed to have risen and fallen over 100 m in 10® years during periods when no polar glaciations occurred. Table 4.3 shows the magnitudes and rates of sea-level change

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Figure 4.12 Computed sequence boundaries and shoreline shifts assuming a variable rate of sea-level fall using the sea-level curves in Figure 4.10 e, f, g, and h.

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100 ISO 200 S U - 0 .0 0 1 S L 2 - 0 .0 0 0 3 5 2 -

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S L 1 -0 .0 S L 2 - 0 .0 0 1 6 5 2 I I s 5 4 I

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Distance of shoreline from hingeilne (km)

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CAUSES; MAGNrrUDES AND RATES OF GLOBAL SEA-LEVEL CHANGE Tim e M echanism Probable Maxim um Interval m axim um m axim um (m a) Magnitude Rato Magnitude Rate (m) (cm/1000 yr). (m) (cm/1000 yr).

Giaclalion 150 1000 250 1000 0.1

Ridge volume 350 0.75 500 1.2 70

Orogeny 70 0.10 150 0.20 70

Sediment 60 0.11 85 0.25 70

Hot spots 50 0.08 100 0.14 70

Flooding of 15 Instantaneous ocean basins

Table 4.3 Causes, magnitude and rates of global sea-level change. (After Pitman and Goiovchenko, 1983).

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associated with their probable causes. It is evident that the rates of change in

sea-level in the absence of glaciation are dominated by changes in mid-ocean ridge volumes. Pitman and Golovchenko (1983), however, point out that the possibility of the occurrence of cyclic fluctuations in sea-level should not be precluded simply because one cannot presently account for a mechanism which might induce such sea-level changes.

The results of the simulations presented in this chapter show that fluctuations in sea-level of the magnitude and character proposed by Vail et al (1977) could not account for the origin of stratigraphie sequences on the Wilcox shelf-margin. The closest approximation to the Wilcox sequences was obtained when a 10® years wavelength and a 5 to 10 m amplitude were used as input' for a third-order sea-level fluctuation. As pointed out earlier, these values do not correspond with any of the values depicted by the Vail sea-level curves. In the hypothetical example simulated above, it was clear that minor fluctuations in the rate of sea-level fall on the order of 0.5 x 10® years could

generate sequences similar to those obsen/ed on the Wilcox margin. The

variability in both local subsidence rates and global sea-level fall seems to be a more plausible explanation for the origin of these sequences than does a cyclic fluctuation in sea-level of the type described by Vail et al (1977). Although any numerical representation of geologic processes involves a degree of oversimplification, this program has enabled one to test the Vail concept of sea-level fluctuations as a means to explain the origin of depositional sequences. It is evident, at least from this study, that even if one

assumes that cyclic sea-level fluctuations do occur, the range of magnitudes

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and amplitudes as they are currently reported in the literature, can be used to predict sequence stratigraphy and shoreline shifts.

BIASED RANDOM-WALK SHOREFACE SIMULATION MODEL

Introduction

The program (STRATSIM) outlined in the preceding section depicts one method of numerical simulation of geologic events. STRATSIM generates stratigraphie sequences based on the premise that the continental shelf profile will attain an equilibrium slope after each time step. Therefore, the program' simulates sequences that are based on simple geometric considerations rather than actual geologic processes. A computer program (DEPSIM) which simulates actual geologic processes will be presented in this section. The purpose of these simulations is to examine the difference between prograding shoreface sequences that form during falling sea-levels from those that form during rising sea-levels. In an examination of preserved sedimentary facies from the Wilcox sheif- margin, two prograding shoreface sequences were recognized. Although similar in overall character (i.e. facies sequences, grain size, and interval thickness), some differences between the two sequences were observed. The major difference occurs in the underlying transitional zone facies. In an idealized prograding shoreface sequence, individual tempestites decrease in thickness basinward and exhibit sharp basal contacts and burrowed upper contacts (Aigner and Reineck, 1982; Brenchley,1985). As the

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shoreface sequence moves basinward, thinner distal tempestites are progressively overlain by thicker proximal components (Fig. 4.13). Therefore, a composite vertical profile through the shoreface sequence would show an upward gradational Increase In thickness and frequency of tempestites. The Increasing frequency of tempestites results In their amalgamation near the upper contact of the facies. In the shoreface sequence which occurs within the unstable portion of the margin (Fordoche field), tempestites within the transition zone facies are commonly amalgamated near the upper contact with the shoreface sandstones (Fig. 4.14a). In addition, the transition zone mudstones exhibit extensive burrowing by bottom-dwelling organisms. The shoreface sequence from the' stable portion of the margin (Lockhart Crossing) exhibits little or no amalgamation of tempestites. Biogenic activity within the mudstone was restricted to a relatively narrow interval (Fig. 4.14b). These differences In the transitional zone facies may reflect temporal changes in the frequency of storms which occurred at these two locations.

Heward (1981) suggested that progradatlonal shoreface sequences which form during a falling sea-level may differ from the "classic progradatlonal shoreface model". In contrast to the distinctive coarsening upward shoreface sequence (Bernard et al, 1959; Bernard et al, 1962; Tavener-Smlth, 1982), he suggested that shoreface sequences which form during a falling sea-level will have a sharp basal contact. Computer program DEPSIM Is used to determine whether such differences do In fact occur.

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PROXIMALITY TRENDS SHELF MUD FACES |TRANS1TIOn|C0ASTAL TWCKEm^ SEQUENCE

wv of ih o r« t*e » •vtrag* «torma

wav* baa# of rnsiof ttorms

GRAIN SIZE BED THICKNESS amalgamation

% TEMPESTITE FREQUENCY •

X - LAMINATION

BIOTURBATION

parautochthonous mimad fauna SHELL LAYERS

Figure 4.13 Conceptual model of shoreface and transition zone facies. (After Aigner, 1985).

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13,170

13,100 . mmh.

b 10,600

13,200 10,610

&o 13,210 10,620 -11 ■ ' / j ) 13,220 - i 13,230 10,640

13,240 FT y 10,650 -

13,250 10,660 J.

13,260 Figure 4.14 Comparison of shoreface sequences from two sheif-margin sandstone bodies. a) Sun N. Smith, Jr. #8 core from Fordoche field (unstable shelf- margin). b) Sun Grown Zellerbach #1 from Lockhart Crossing/Livingston field (stable shelf-margin). In the vertical profile from the unstable margin, tempestites underlying the main shoreface are thicker, (amalgamated) and exhibit a greater degree of bioturbation than those from the stable margin sequence.

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Program structure

Program DEPSIM is a biased random-waik model. Biased refers to the fact that the probabilities of occurrence of certain geologic processes are not truly random, but that some have a higher probability of occurrence than others. Inputs to the program are as follows: sea-level change per time interval; sediment volume delivered to the shoreface; probability of sediment supply switching; probability of storms occurring; and probability of a storm of a certain magnitude occurring. The program is partially based on a principal outlined by Harbaugh and Bonham-Carter (1970) in which a continental shelf profile is represented by a' series of cells of equal width (0.5km) (Fig. 4.15). Water depth at any point on the shelf profile is represented by the thickness of individual cells. Variation in the thickness of each cell is determined by the volume of sediment delivered and the relative change in sea-level.

The program includes the same option as STRATSIM to determine sea- level change for each iteration; however, for the purposes of the experiments presented here, constant sea-level change values are provided as input. After defining the sea-level curve, the program begins the main iteration which represents a one year time interval. The first procedure within the main iteration determines whether sediment is delivered to the shoreface from an external (fluvial) source. This procedure was included for the purpose of simulating autocyclic sedimentation similar to that which has occurred within the modern Mississippi delta complex over the last 7x10^ to 9x10^ years. Delta lobe

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Sediment input

Sea Level

Deposition Shelf profile

Subsidence

Figure 4.15 Schematic of block structure used in the DEPSIM program. The shelf profile is defined by the midpoint of each block. Varying the thickness of each block enables simulation of changes in profile geometry.

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switching has occurred on the average of every 10^ years over this time period (Frazier, 1974).

Simulation of sediment switching is accomplished by first generating a random number between 0 and 1. If the random number is between 0 and 0.001 (i.e. there is a 0.1% chance of sediment switching), the sediment supply delivered to the shoreface is switched on or off depending on the initial condition.

The locations of the shoreline, transition zone, and storm wave base are determined at every time step. Depths for the upper limit of the transition zone from modern examples of beach to shelf profiles range between two and twenty meters (Bernard et al, 1959; Curray et al, 1969; Reineck and Singh,' 1971; Reineck and Singh, 1980; Howard and Reineck, 1981) (Fig. 4.16). -Average depth for the landward limit of the transition zone is ten meters (Reineck and Singh, 1980). The location of storm wave base is dependent on the wave regime. A storm wave with a period of six seconds would result in the

development of a storm wave base at approximately twenty meters (C.E.R.C, 1977; Komar, 1973). The location of these zones is dependent upon sedimentologic and hydrodynamic characteristics of the shoreface. The depth values (10 and 20 m) used in DEPSIM are intended to simulate a sand- dominated shoreface in a moderate to high wave-energy regime. Sediment delivered to the shoreface is distributed between the shoreline and the landward limit of the transition zone. In the program presented by Harbaugh and Bonham-Carter (1970), a constant proportionality coefficient (k) was used to simulate a geometric decrease in the volume of sediment delivered to each cell along the entire length of the profile, in reality, however.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ::o ■DCD O Q. C g Q.

■D CD

C/) C/)

8

(O'

OFFSHORE TRANSITION SHORE FACE FORE SHORE BACK SHORE DUNES (SHELF MUD) ZONE

3"3 . HWL CD LWL ■DCD O WAVE BASE Q. C a 3o BEACH BAR BERM "O LONGSHORE TROUGH RUNNEL o BAR (RUNNEL)

CD Q. Figure 4.16 Schematic cross-section through a modern beach shelf profile. (After Reineck and Singh, 1980). ■D CD

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most sediment delivered to the shoreface is deposited between the shoreline and landward limit of the transition zone (Komar, 1973, 1976). Consequently, by using the general expression for a geometric series it was possible to ensure that at least 99% of the sediment delivered to the shoreface was deposited between these two cell locations. The geometric decrease in the volume of sediment deposited in each cell between the shoreline and landward limit of the transition zone is maintained. As sediment is added to each cell, the depth at each location on the shelf profile is adjusted. The program constantly checks to ensure that aggradation does not occur above sea-level. If a particular cell (J) has reached sea-level, excess sediment is transported into the next cell (J+1) and added to the' computed sediment input volume (SEDQj+i ) for that cell (J+1 ). In the situation where excess sediment exists after the final shoreface cell has been filled, the remaining sediment is distributed throughout the transition zone. After simulation of sediment deposition within the shoreface, the program detemines whether or not a storm will occur during the iteration. The probability of a storm occurring has been arbitrarily set at 0.05 or a 5% chance. If a storm is not simulated, a uniform layer of mud is deposited along the entire length of the profile from the landward limit of the transition zone seaward. If a storm does occur, the program generates another random number to determine the magnitude of the storm and the resultant sedimentological response of the shelf. Given that a storm has occurred, there is a 75% probability that the storm will generate a tempestite that is 20 cm thick. There is a 20% chance that a storm will generate a 30 cm thick tempestite and a 5% chance that a 40 cm thick tempestite will be generated. These values are anomolously large

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compared to those observed on the Wilcox shelf-margin; however, they have been used to facilitate recognition of the individual tempestites on the computer generated plots.

Having determined the magnitude of a storm, the program then simulates the deposition of the tempestite seaward of the transition zone. The conceptual model for tempestite deposition is based on that of Aigner, 1985 and Aigner and Reineck, 1982. The thickness of the individual tempestites is decreased by 0.002 cm per cell to simulate the decrease in thickness of the beds seaward. Following deposition of the tempestite, a uniform layer of mud is deposited along the shelf profile seaward of storm wave base. The program

then adjusts sea-level and subsides the entire shelf profile by a specified' subsidence value prior to initiating simulation of the next time interval. An option which will simulate the effect of syndepositional faulting (growth-faults) on the stratigraphie sequence has been included in the program. The location of a growth-fault is defined by the distance between two cells along the shelf profile. Maximum subsidence within the growth-fauit

occurs at the cell closest to the shoreline and decreases to zero at the basinward extent of the zone. The subsidence rate of the growth-fault is provided as program input.

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Program results

Introduction

For the purposes of depicting specific relationships between key variables in the simulation experiments, a constant random number seed was

used in all tests. The use of a constant random number seed means that differences observed between calculated sequences will be due to changes In the rates and magnitude of specific processes as opposed to random variability. In addition, the option for sediment switching was not invoked in order to avoid the possibility that random variability would obscure' fundamental relationships. The program was used to conduct three basic experiments. These experiments are as follows: a) examination of temporal variation in sandbody geometry, b) examination of shoreface response to variable rates of sea-level change, and c) comparison of transition zone facies which formed under rising versus falling sea-levels.

Temporal variation in the sandbodv aeometrv

Figure 4.17 shows the results of a simulation of a prograding shoreface which formed during a falling sea-level. In this simulation, eustatic sea-ievel was falling at a rate of 0.8 cm y r1 . This rate is at the upper limit of the range of values for rates of change in eustatic sea-level (.Nummedal, 1983). It is comparable to rates of sea-level change reported to have occurred during the

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Figure 4.17 Simulated progradatlonal shoreface sequence formed during a relative sea-level fall. a) Shoreface after 10 years simulation. b) Shoreface after 100 years simulation. c) Shoreface after 750 years simulation. d) Shoreface after 750 years simulation with subaerial erosion of exposed facies.

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Holocene period by Coiquhoun et al (1981). Basin subsidence was set at zero and the initial sediment supply to the shoreface was set at 10 m 3 yr\ Figure 4.17a shows the position of the shoreline and the resultant facies sequences after 10 years have been simulated. The figure shows the occurrence of a period of rapid progradation of the shoreface (13 km) and the development of a thin transition zone facies. After 100 years (Fig. 4.17b), the annual rate of shoreline migration has decreased significantly (the shoreline has been translated only 3 km seaward from the previous location). This reduction in the rate of shoreline migration reflects progradation into progressively deeper water. In this simulation, one can clearly see the development of successive tempestites underlying the main sandstone facies.' Figure 4.17c shows the complete sequence after 750 years. The shoreline has migrated 33 km seaward from the initial position and the shoreface sands have been displaced 6 m below their original level. Figure 4.17d shows how the sequence would appear after subaerial erosion had removed the exposed sequence located landward of the shoreline.

Shoreface response to variable rates of sea-level change

A series of simulations were conducted to examine the effect of variable rates of sea-level rise on the development of the shoreface sequence over a 500 year period. Sediment supply (10 m3 y r i) was constant and basin subsidence did not occur. Figure 4.18a shows the simulated shoreface sequence for a sea-level rise of 0.1 mm y rT A gradual stratigraphie climb of the shoreface is evident as

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Figure 4.18 Comparison of progradational shoreface sequences which formed under variable rates of sea-level rise. a) shoreface sequence for a sea-level rise of 0.1 mm y r i b) shoreface sequence for a sea-level rise of 1.2 mm y r i c) shoreface sequence for a sea-level rise of 5.0 mm yr^

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Distance seaward (km)

S ea-level

S *'“■ a .

S ->»• Sea-level rise 0.1mm yr Sediment supply 10 m \r' No subsidence - n . Time interval 500 yrs -as.

Distance seaward (km) IS. 80 . t _

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Distance seaward (km) IB. _ i _ Seo-l6vel|

Sea-level rise 5 mm yr' Sediment supply 10 m^yr' No subsidence Time interval 500 yrs

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time increases. An increase in the rate of sea-level change to 1.2 mm yr-i creates a significant reduction in the magnitude of shoreface migration (Fig. 4.18b). The aggradational component of the shoreface sequence which occurs landward of the shoreline is clearly demonstrated. Increasing the rate of sea- level rise to 5 mm yr-"* results in the further reduction of the progradational component and an increase in the aggradational phase (Fig. 4.18c). These simulations, in effect, replicate the conditions which gave rise to the Galveston Island progradational shoreface sequence. By varying the amount of sediment delivered to the shoreface, one can calibrate the rates of shoreline migration so that they will correspond with the observed rates.

Comparison of transition zone facies which formed under rising versus falling sea-levels.

The final series of experiments were conducted to determine how a prograding shoreface sequence that formed under a falling sea-level would differ from one that formed under a rising sea-level. More specifically, one objective of this series of experiments is to identify whether differences exist between the transition zone facies of the two shoreface sequences. Figure 4.19 shows the simulated shoreface sequences that would result from progradation during a rising sea-level, falling sea-level, and sea-level stilistand. The degree to which the underlying transition zone facies is translated seaward is a direct consequence of the rate and direction of sea- level change. Figure 4.20 shows the occurrence and magnitude of simulated storms. Figure 4.21a is a close-up view of the transition zone facies and shows that during a rising sea-level (1.2 mm y r i; sediment input 10 m3 y ri), the

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Figure 4.19 Comparison of progradational shoreface sequences which formed during a sea-level rise, sea-level stilistand, and sea-level fall.

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OCCURRENCE AND INTENSITY OF STORMS FOR 500 YEAR SIMULATION TESTS

4 ,54

4. Prob. of storm 5®/

>, 3 5. œ 3. c

.5.

0. I ™ I * " I 0 100 150 200 250 300 350 400 450 500 Time (years)

Figure 4.20 Frequency of occurrence and intensity (0-3; O=lowest intensity) of simulated storms depicted in Figure 4.19.

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Figure 4.21 Close-up views of the transition facies of each of the shoreface sequences shown in Figure 4.19. a) rising sea-level b) sea-level stilistand c) falling sea-level

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a

Location of profile shown wi fig. 4.22a

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Location of profile shown in fig. 4.22c

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upward translation of the facies is readily apparent and the basinward translation of the transition zone facies is less than 6 km. Figure 4.21b depicts a close-up view of the transition zone facies which formed during progradation associated with the sea-level stilistand. A minor downward translation of the shoreface sands (less than 10 to 20 cm) occurs in response to a relative sea- level fall resulting from the influence of a high sediment influx. Figure 4.21c is a close-up view of the transition zone facies which formed during a falling sea- level over a 500 year period. Sea-level fall was 0.8 cm y rf and sediment supply was 10 m3 y ri. In this case, the transition zone facies exhibits a greater basinward translation than shown in the previous situation. Over the 500 year period, the transition zone facies extends along a 15 km wide zone as opposed' to 7 km for a simulated sea-level stilistand. This variability in the degree of basinward translation of the shoreface has a profound effect on the resultant vertical stratigraphie profile at any point which underlies the main shoreface interval. Figure 4.22 is a representation of the synthetic vertical stratigraphie profiles which formed under different sea-level change conditions. Figure 4.22a depicts the amalgamation of tempestites which formed during the simulated rise in sea-level (see Fig. 4.21a for location of the profile). In figure 4.22b, the stratigraphie profile represents a sequence which formed during a relative stilistand (see Fig. 4.21b for location of the profile). Twenty tempestites occur within a 5 meter interval and there is a general upward increase in the average thickness of each tempestite towards the main shoreface sandstone. The stratigraphie profile shown in figure 4.22c formed during a falling sea-level (see Fig. 4.21c for the location of the profile). A total of 13 tempestites occur

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Figure 4.22 Comparison of vertical profiles through the transition zones shown ■ D CD in Figure 4.21. a) rising sea-level (/) b) sea-level stilistand c) falling sea-level Note that the number of tempestites, thickness, and potential for amalgamation are much greater In the rising sea-level model (a) r o than In the falling sea-level model (c). j i . 245

within the 5 meter interval shown on the profile. Most tempestites are separated by a mudstone interval of almost equal thickness.

Discussion

The modern examples of regressive shoreface sequences described by Bernard et al (1959), Bernard et al (1962), and Reineck and Singh (1971; 1980) represent a depositional system which formed during a rising eustatic sea-level. With the exception of some hypothetical models (Heward, 1981; Reinson, 1984) no facies model currently exists to account for the development of a regressive shoreface which formed during a falling sea-level. There exists an obvious need for such a model since the rock record must contain at least an equal number of such regressive shoreface sequences.

Program DEPSIM has allowed the characterization of facies model for the prograding shoreface which would form during a falling sea-level. The results of the program suggest that an inherent difference occurs between the transition facies of a sequence which forms during a falling relative sea-level as opposed to one which forms during a rising relative sea-level. The greater basinward translation of the shoreface during a falling sea-level results in an apparent reduction in the concentration of tempestites per unit interval in comparison to the sequence which formed during a rising sea-level. This model for shoreface progradation appears to accurately reflect the deposition of the '1st Wilcox' sandstone. The '1st Wilcox' is a sandstone body which extends 16 to 23 km updip and 65 km along strike. It is assymetric in the basinward direction. The sandstone body is characteristic of a typical progradational shoreface sequence, with the exception of the transition zone

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facies which is poorly developed. On the basis of the simulations performed, the depositional model suggests that initial rapid progradation occurs as sediment supply keeps pace with the falling sea-level. Progradation continues to the point at which a relative sea-level rise is initiated. Penecontemporaneous erosion of the exposed portion of the shoreface sequence results in the creation of a wedge-shaped sandbody (i.e. assymetric in the basinward direction) or 'truncated progradational shoreface sequence'. A rapid sea-level rise would preserve the pre-transgressive morphological character of the sandbody. A gradual rise would result in extensive erosional shoreface retreat and obliteration of the shoreface facies.

In light of the proposed model and the preservation of the assymetric' profile, the '1st Wilcox' sandstone appears to have experienced a rapid rise in sea-level after the progradational phase ended (Fig. 4.23). Such a condition would not be unusual at the shelf-margin since the maximum rate of subsidence occurs near shelf-break and gentle slopes (0.1 to 0.2°) can result in rapid rates of sea-level change (Pitman and Golovchenko, 1983). The difference between the two Wilcox shoreface sequences (Lockhart Crossing and Fordoche) may be due to the fact that the Fordoche field sequence formed during a relative rise in sea-level. This relative rise may have resulted when local subsidence in the unstable portion of the margin (Fordoche) was much greater than that from the stable margin. Consequently, even though eustatic sea-level may have been falling, the increased subsidence resulted in a relative rise. Both programs presented in this chapter enable the evaluation of geologic models at two contrasting scales. While any program has inherent

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Sea Level Recession and Abundant Sediment Supply

Erosion and modification

Shoreline sands. g Regressive shoreface 3 clays,silts and sands.? X / JOlder depbsils.

;««îg;î5|};

...

Figure 4.23 Conceptual model for progradation and preservation of a truncated regressive shoreface which formed during a falling sea- level.

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limitations when attempting to simulate actual geologic processes, It is believed that the first program presented has provided valuable insight into processes which affect the facies architecture of shallow marine clastic depositional systems. In addition, the second program has enabled the simulation of facies sequences associated with a depositional event which may have few, if any, modern analogues.

CONCLUSIONS

Results of the first computer program which simulated the development of

clastic stratigraphie sequences on a passive continental shelf-margin yielded the following conclusions:

1) Third and fourth-order sea-level fluctuations similar to those described by Vail et al (1977) could not account for the occurrence of stratigraphie sequences on the Wilcox shelf-margin.

2) The closest approximation to the Wilcox sequences was simulated

when a third-order sea-level cycle with a wavelength of 10® years and amplitude of 5 to 10 m were used as input. These values do not correspond with any published values for sea-level cycles.

3) The use of a hypothetical sea-level curve that exhibited

fluctuations in the rate of fall over a 5 x 1 0 ^ year period generated a series of sequences similar to those observed on the Wilcox margin.

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4) Normal variability in the rate of eustatic sea-level fall appears to be a simpler and more plausible explanation for the occurrence of the Wilcox sequences as opposed to a cyclic sea-level fluctuation of the magnitude described above (see conclusion number 2).

Results from the second computer program written to simulate progradation of a shoreface from one of the Wilcox sequences provided some general insight into the differences in facies which may occur between rising and falling sea-level.

1) During a rising sea-level, the transition zone remains within a' relatively narrow region. This situation results in stacking or amalgamation of individual tempestites, and a greater opportunity for bottom-dwelling organisms to bioturbate the mudstones.

2) During a falling sea-level, extensive basinward translation of facies occurs and, therefore, reduces the potential for amalgamation of tempestites and extensive biogenic activity.

3) An increase in the rate of sea-level rise results in the reduction of the width of the transition zone. A vertical profile through the sequence would reveal a relatively thick transition zone facies.

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4) An increase in the rate of sea-level fall would result in an increase in the width of the transition zone. A vertical profile through the sequence would show a relatively thin transition zone facies.

REFERENCES

Aigner, T. and Reineck, H. E., 1982, Proximality trends in modern storm sands from Helgoland Bight (North Sea) and their implications for basin analysis: Senckenbergiana marit, 14, p. 183-215. Aigner, T., 1985, Storm Depositional Systems: Dynamic Stratigraphy in Modern and Ancient Shallow-Marine Sequences, Springer-Verlag, Berlin, 174 p. Bernard, H. A., Major, 0. P., and Parrot, B. S., 1959, The Galveston Barrier Island and environs - a model for predicting reservoir occurrence and trend. Gulf Coast Assoc. Geol. Soc. Trans., v. 9, 221-224. Bernard, H. A., LeBlanc, R. J., and Major, 0. P., 1962, Recent and Pleistocene Geology of southeast Texas and guidebook of excursion: in Geology of the Gulf Coast and Central Texas and Guidebook of Excursions, Houston Geol. Soc., Houston, Texas, p. 175-224. Brenchley, P. J., 1985, Storm influenced sandstone beds: Modern Geol., v. 9, p. 369- 396.

Coastal Engineering Research Center, 1977, Shore Protection Manual, U.S. Govt. Printing Office, Washington, D.C., 3 vols. Colquhoun, D. J., Brooks, M. J., Michie, J., Abbott, W. B., Stapor, P. W., Newman, W., and Pardi, R. R., 1981, Location of archaeological sites with respect to sea-level in the southeastern : Striae, v. 14, p. 144-150.

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Curray, J. R., Emmel, F. J., and Crampton, P. J. S., 1969, Holocene history of a strand plain, lagoonal coast, Nayarit, Mexico: in A. A. Castanares and F.

B. Phleger, eds.. Coastal Lagoons, A Symposium, Universidad Nacional Autonoma, Mexico, p. 63-100. Ewing, M. and Donn, W. L, 1958, A theory of ice ages: Science, v. 127, p. 1159- 1162.

Frazier, D. E., 1974, Depositional-episodes: Their relationships to the Quaternary stratigraphie framework in the northwestern portion of the Gulf Coast basin: Geological Circular, 74-1, Texas Bureau Economic Geology, Univ. Texas, Austin, Texas, 28 p.

Haq, B. U., Hardenbol, J., and Vaii, P. R., 1987, Chronology of fluctuating sea levels since the : Science, v. 235, p. 1156-1167. Harbaugh, J. W. and Bonham-Carter, G., 1970, Computer Simulation in Geology, John Wiley & Sons, New York, 575 p. Reward, A. P., 1981, A review of wave-dominated clastic shoreline deposits: Earth Sci. Rev., v. 17, p. 223-276. Howard, J. D. and Reineck, H. E., 1972, Georgia coastal region, Sapelo Island, USA: Sedimentology and biology, IV, Physical and biogenic sedimentary structures of the nearshore shelf: Senckenbergiana marit., 4, p. 81-123. Howard, J. D. and Reineck, H. E., 1981, Depositional facies of high-energy beach-to-offshore sequence-comparison with low-energy sequence: Am. Assoc. Petroleum. Geologists Bull., v. 65, p. 807-830. Komar, P. D., 1973, Computer models of delta growth due to sediment input from rivers and longshore transport: Geol. Soc. America Bull., v. 84, p. 2217-2226.

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Komar, P. D., 1976, Beach Processes and Sedimentation, Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 429 p. Miall, A. D., 1984, Principles of Sedimentary Basin Analysis, Springer-Verlag, New York, 490 p.

Nummedal, D., 1983, Rates and frequencies of sea-level changes; A review with an application to predict future sea-levels in Louisiana: Gulf Coast Assoc. Geol. Soc. Trans., v. 33, p. 361-366. Pitman, W. 0., 1978, Relationship between eustacy and stratigraphie sequences of passive margins: Geol. Soc. America Bull., v. 89, p. 1389- 1403. Pitman, W. 0. and Golovchenko, X., 1983, The effect of sealevel change on the shelfedge and slope of a passive margin: In D. J. Stanley and G. T. Moore, eds.. The Sheifbreak - Critical Interface on Continenm! Margins, Soc. Econ. Paleontologists. Mineralogists. Spec. Pub. No. 33, p. 41-58. Reineck, H. E. and Singh, I. B., 1971, Der Golf von Gaeta/ Tyrrhenisches Meer. 3. Die Gefuge von Vorstrand-und Sehelfsedimenten: Senckenbergiana marit, 3, p. 185-201. Reineck, H. E. and Singh, I. S., 1980, Depositional Sedimentary Environments - With Reference to Terrigenous Clastics, 2nd ed., Springer-Verlag, New York, 549 p. Reinson, G. E., 1984, Barrier island and associated strand-plain systems: in R. G. Walker, ed., Facies Models, 2nd ed., Geosci. Can. Reprint Series 1, p. 119-140.

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Tavener-Smith, R., 1982, Prograding coastal facies associations In the Vryheld Formation (Permian) at Effingham Quarries near Durban, South Africa: Sedimentary Geol., v. 32, p. 111-140.

Vail, P. R., MItchum, R. M., and Thompson, S., Ill, 1977, Seismic stratigraphy and global changes In sea level, Part 3: Relative changes of sea level from coastal onlap: in C. E. Payton, eds.. Seismic Stratigraphy- Applications to Hydrocarbon Exploration, Am. Assoc. Petroleum Geologists Memoir 26, p. 63-97.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. BIBLIOGRAPHY

Adams, G. S., 1985, Depositional history and diagenesis of the middie Glen Rose reef complex (Lower Cretaceous), East Texas and Louisiana; Baton Rouge, Louisiana State University, Master’s thesis, 200 p. Addy, 8. K. and Buffler, R. T., 1984, Seismic stratigraphy of the shelf and slope, northeastern Gulf of Mexico: Am. Assoc. Petroleum Geologists Bull., v, 68, p. 1782-1789. Aigner, T., 1985, Storm Depositional Systems: Dynamic Stratigraphy in Modern and .Ancient Shallow-Marine Sequences, Springer-Verlag, Berlin, 174 p. Aigner, T. and Reineck, H. E., 1982, Proximality trends in modern storm sands from Helgoland Bight (North Sea) and their implications for basin analysis: Senckenbergiana marit., 14, p. 183-215. Aibach, D. 0., 1979, The depositional history of the uppermost Wilcox (lower Eocene) of west-central Beauregard Parish, Louisiana: Baton Rouge, Louisiana State University, Master’s thesis, 98 p.

Almgren, A. A., 1978, Timing of Tertiary submarine canyons and marine cycles of deposition in the southern Sacramento Valley, California://? D. J. Stanley and G. Kelling, eds.. Sedimentation in Submarine Canyons, Fans, and Trenches, Dowden, Hutchinson, & Ross, Inc., Stroudsburg, Pa, p. 276-291.

Andersen, H. V., 1960, Geology of Sabine Parish: Louisiana Geological Survey, Geological Bulletin No. 34, 164 p.

254

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Anisgard, H. W., 1970, Causes of dominantly arenaceous foraminiferal assemblages In downdip Wilcox of Louisiana: Gulf Coast Assoc. Geol. Soc. Trans., v. 20, p. 210-217. Berg, O. R., 1982, Seismic detection and evaluation of delta and turbidite sequences: Their application to exploration for the subtle trap: Am. Assoc. Petroleum Geologists Bull., v. 66, p. 1271-1288. Berg, O. R. and Woolverton, D. G., 1984, Seismic Stratigraphy II: An Integrated Approach to Hydrocarbon Exploration, Am. Assoc. Petroleum Geologists Memoir 39, 276 p. Berg, R. R. and Tedford, F. J., 1977, Characteristics of Wilcox gas reservoirs, northeast Thompsonville Field, Jim Hogg and Webb Counties, Texas: Gulf Coast Assoc. Geol. Soc. Trans., v. 27, p. 6-19. Bernard, H. A., LeBlanc, R. J., and Major, C. F., 1962, Recent and Pleistocene Geology of Southeast Texas and Guidebook of Excursion: in Geology of the Gulf Coast and Central Texas and Guidebook of Excursions, Houston Geol. Soc., Houston, Texas, p. 175-224.

Bernard, H. A., Major, C. F., and Parrot, B. S., 1959, The Galveston Barrier Island and environs - a model for predicting reservoir occurrence and trend: Gulf Coast Assoc. Geol. Soc. Trans., v. 9, p. 221-224. Bornhauser, M., 1948, Possible ancient submarine canyon in southwestern

Louisiana: Am. Assoc. Petroleum Geologists Bull., v. 32, p. 2287-2290. Bouma, A. H., Stelting, C. E., and Coleman, J. M., 1984, Mississippi fan: Internal

structure and depositional processes: Geo-Marine Letters, v. 3, p. 147- 153.

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Bourgeois, J., 1980, A transgressive shelf sequence exhibiting hummocky stratification-the Cape Sebastian Sandstone (upper Cretaceous), southwestern Oregon: Jour. Sed. Petrology, v. 50, p. 681-702. Boyles, J. M., Kauffman, E. G., Kiteley, L W., and Scott, A. J., 1981, Depositional Systems Upper Cretaceous Mancos Shaie and Mesaverde Group, Northwestern Colorado -Fall Field Trip Guidebook, Rocky Mountain Section Soc. Econ. Paleontologists and Mineralogists Part 1,81 p. Brenchley, P. J., 1985, Storm influenced sandstone beds: Modern Geology., v. 9, p. 369-396. Bruce, 0. H., 1973, Pressured shale and related sediment deformation: Mechanism for development of regional contemporaneous faults: Am. Assoc. Petroleum Geologists Bull., v. 57, p. 878-886. Busch, D. A., 1975, Influence of growth faulting on sedimentation and prospect evaluation: Am. Assoc. Petroleum Geologists Bull., v. 59, p. 217-230. Carter, G. H., 1978, A regressive barrier and barrier-protected deposit: Depositional environment and geographic setting of the Late Tertiary Cohansey Sand: Jour. Sed. Petrology, v. 48, p. 933-950. Caughey, C. A., 1975 a. Pleistocene depositional trends host valuable Gulf oil reserves: Oil and Gas Jour., v. 73, no. 36, p. 90-94. Caughey, C. A., 1975 b. Pleistocene depositional trends host valuable Gulf oil reserves: Oil and Gas Jour., v. 73, no. 37, p. 240-242. Christina, C. C. and Martin, K. G., 1979, The lower Tuscaloosa trend of south- central Louisiana, 'You ain't seen nothing till you've seen the Tuscaloosa': Gulf Coast Assoc. Geol. Soc. Trans., v. 29, p. 37-41.

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LISTINGS OF COMPUTER PROGRAMS STRATSIM AND DEPSIM

273

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 274 C PROGRAM DEPSIM C C A PROGRAM TO SIMULATE THE DEVELOPMENT OF PROGRADATIONAL 0 SHOREFACE SEQUENCES AND THE INTERACTION OF EUSTATIC C SEA-LEVEL CHANGE, VARIATION IN SEDIMENT SUPPLY. BASIN C SUBSIDENCE AND SYNDEPOSITIONAL FAULTING. C C C WRITTEN BY C C PHILIP LOWRY C DEPT. OF GEOLOGY C LOUISIANA STATE UNIVERSITY C C VERSION OF OCTOBER 1986 c c PROL = LENGTH OF ENTIRE PROFILE 50 KM c SHFB = LOCATION OF SHELF BREAK 30 KM c GRDSH= GRADIENT OF SHELF .1 DEGREES c GRDSL= GRADIENT OF SLOPE 1.5 DEGREES c CEL = LENGTH OF EACH CELL 0.5 KM c TZ = DEPTH OF TRANSITION ZONE 10M c SWB = DEPTH OF STORM WAVE BASE 20M c NCELS= NUMBER OF BLOCKS/CELLS 100 c PRBST= PROBABILITY OF A STORM 5% c PRBSST= PROB. OF STORM WITH MAGNITUDE M 75,20,5% c SEDQ= SED SUPPLY TO SHOREF AT TIME J M"3/YR M*‘ -1 c SEDI = INITIAL SUPPLY OF SED. TO SHORF M**3A'R M**-1 c SMUD RATE OF MUD DEPOSITION 5 MM/YR c PRBSW= PROB. OF SED SUPPLY SWITCHING 0.001 c NIT = LENGTH OF EACH ITERATION 1 YR c NTIME TOTAL SIMULATED TIME YEARS c RSS = RATE OF UNIFORM SUB CM/YR c MORESUB= GROWTH FAULTING Y/N 0/1 c ICEL = UPDIP LOCATION OF GF c KCEL = DOWNDIP LOCATION OF GF c SUB(J)= SUBSIDENCE AT CELL J CM/YR c NCYCLES =# OF VAIL TYPE SEALEVEL CYCLES 5 C. SLAMP(J)= AMPLITUDE OF CYCLE J 100,80,80,70,1 M c SLWVL(J)= WAVELENGTH OF CYCLE J 250,60,10,4,.00003 MA c IDUM = RANDOM # SEED (2**31 )-1 2147483647

DIMENSION X(101), DEP(101,4001),SAMPLE(4001},FREQ(50),UB(50) DIMENSION Z2SAMPLE(4001 ),Z3SAMPLE(4001 ),DD(101 ),SLAMP(5) DIMENSION SLWVL(5),SLC(4001 ),SLP(4001 ),NSHOR(4000)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 275

INTEGER PROBD.PLRQ DATA SUMP/100..80..80..70.,1.0/ DATA Pi/3.141592654/ DATA SLWV1_/250000000..60000000..10000000..40000..300./ OPEN(UNIT=7. FILE='DATA0UT.DAT.8TATU8='NEW') OPEN(UNIT=8. FILE='PLANTEST.DAT',STATU8='0LD') WRITE(6.14) WRITE(6.19) READ{8.*) PLRQ.PROBD,PARMI .PARM2

C SET CONSTANTS

SEDQ=SEDI TZ=10. SWB=20. NIT=1 IDUM=2147483647 PROL=50 NCELS=100 SMUD=0.005 SHFB=30 GRDSHE=.001745331 GRDSL=0.0261859 CEL=(PROL/NCELS)

C CALCUUTE THE DEPTH VALUES AT EACH CELL

KN=0

DO 10 FK=O.SHFB.CEL KN=KN+1 X(KN)=KN DEP(KN.1 )=(FK*GRDSHE)*1000. 10 CONTINUE

SHFBPL=SHFB+CEL PROLMN=PROL-SHFBPL C0NDEP=DEP(KN.1)

DO 20 FK=CEL.PROLMN,CEL KN=KN+1 X(KN)=KN DEP(KN. 1 )=CONDEP+(FK*G RDSL)*1000. 20 CONTINUE

C INTERACTIVE DATA INPUT

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 276 WRITE(6,781) 781 F0RMAT(1 X,'Enter the range of cells to represent the shelf) READ(5,*) XMIN,XMAX WRITE(6,782) 782 F0RMAT(1 X,'Enter the max. and min. depth values (depth is neg.)') READ(5,*) YMAX.YMIN WRITE(6,287) 287 F0RMAT(1 X,'Enter the total time period of the simulation (yrs,)') READ(5,*) NTIME C write(6,288) C 288 F0RMAT(1 X.'Do you want a constant sea-level chanae? Y=1 N=0') SLQU=1 C READ(5,*) SLQU IF(SLQU.EQ.O) GOTO 883 WRITE(6.289) 289 F0RMAT(1X,'Enter the constant rate of sea-level change (+=Rising)') READ(5,*) SL WRITE(6,292) 292 F0RMAT(1x,'Enter the subsidence rate and sediment input') READ(5,*) RSS,SEDI SEDQ=SEDI WRITE(6,267) 267 F0RMAT(1 X.'Do you want to simulate growth-faulting? 0=N, 1 =Y') READ(5,*) MORESUB IF(MORESUB.EQ.O) GOTO 266 WRITE(6,268) 268 FORMAT(1X,'Enter location of fault and subsidence rate') READ(5,*) ICEL,KCEL.GFSUB

C SET UP INITIAL PLOTTING WINDOW

266 LTYPE=1 CALL SETW(0.1,0.9,0.1,0.7,XMIN,XMAX,YMIN,YMAX,LTYPE) CALL LABM0D(7H(F10.0),7H(F10.0),10,10,0,0,10,-30,0) CALL OPTN(2HCO,3HBLA) CALL HALFAX{10,0,10,0,XMIN,YMAX,1.1)

C LINEAR SEA-LEVEL DATA

NITS=1 JN=0 DO 801 KKI=1 ,NTIME,NITS JN=JN+1 SLC(JN)=SL 801 CONTINUE GOTO 759

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 277 883 CONTINUE

C DEFINE THE SEA LEVEL CURVE

JN=0 PII=PI/2 NITS=1 DO 360 LJ=1,NTIME,NITS JN=JN+1 SL=0. DO 120 KKJ =1,4 CON=PII SL=SL+SLAMP(KKJ)*(SIN((2*PI*LJ)/(SLWVL(KKJ))+C0N)) 120 CONTINUE SLC(JN)=SL SLP(JN)=JN 360 CONTINUE WRITE(6,*) JN

C CALL EZXY(SLP.SLC,jn,'SEA LEVEL CURVES’) 759 CONTINUE

SLLP=0

C...... START MAIN LOOP FOR EACH INTERVAL OF TIME ....

DO 8888 J=1,NTIME,NIT

C...... Check to see If sediment supply switches (ON or OFF)

C.PROBD =1 For uniform random numbers (PARMI = MIN: PARM2 = MAX) C PROBD =2 Normal random numbers (PARMI = MEAN: PARM2 = ST. DEV) C C CALL SAM(PR0BD,1 ,IDUM,PARM1 ,PARM2,ZSAMPLE)

C SAMPLE(J)=ZSAMPLE IF(SAMPLE(J).GT.0.001) GOTO 110 G O T0110 IF(SEDQ.EQ.O.) GOTO 102 IF(SEDO.GT.O.) GOTO 103 102 SEDQ=SEDI

GOTO 104

103 SEDQ=0. 104 WRITE(7,101) J,SEDQ C IF(P 0JD.NE.2) GOTO 105 C WRITE(7,301 ) PARMI ,PARM2

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 278 C 105 WRITE(7.300)(FREQ(M),UB(M),M=1,50)

C...... FIND THE LOCATION (CELL) OF FAIRWEATHER AND STORM WAVE BASE C NK1 =CELL WHICH REPRESENTS LOCATION OF TRANSITION ZONE C NK2 = ” " " " " STORM WAVE BASE C NK3 = ...... SHORELINE 110 NN=0

DO 40 K=1 ,KN IF(NN.E0.1)G0T0 45 CALCD=DEP(K,J)-SLLP IF(CALCD.LT.TZ) GOTO 40 NK1=K NN=NN+1 40 CONTINUE

45 CONTINUE

INN=Q

DO 50 K=1 .NCELS IF(INN.EQ.1)G0T0 55 CALD=DEP(K,J)-SLLP IF(CALD.LT.SWB) GOTO 50 NK2=K INN=!NN+1 50 CONTINUE

55 CONTINUE

DO 60 K=1,NCELS OALE=DEP(K.J)-SLLP IF(CALE.GT.O.) GOTO 60 NK3=K 60 CONTINUE

IF(NK3.EQ.O) NK3=1 NSH0R(J)=NK3 C C DETERMINE THE VALUE OF PK WHICH WILL BE USED TO DISTRIBUTE C 99% OF THE SEDIMENT BETWEEN SHORELINE AND TRANSITION ZONE C USES THE GENERAL EXPRESSION FOR A GEOMETRIC SERIES WHERE:

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 279 Sn=({1-A)**N+1)/(1-A)

NKK=NK1-NK3 PK=1.-((0.01)**(1./(NKK+1)))

C C DISTRIBUTE SEDIMENT BETWEEN SHORELINE AND TRANSITION ZONE C THE ROUTINE WILL NOT PERMIT AGGRADATION ABOVE SEA-LEVEL 0 EXCESS SEDIMENT IS DISTRIBUTED INTO THE NEXT CELL AS ADDSED

JN=0 ADDSEDsO.

DO 74 IJ=NK3,NK1 JN=JN+1 SEDDEP=ADDSED+(SEDQ*PKr((1 -PK)**(JN-1 )) DEP(IJ,J+1 )=DEP(IJ,J)-SEDDEP CALF=DEP(IJ,J+1)-SLLP IF(CALF.GT.O.O) GOTO 76 ADDSED=ABS(DEP(IJ,J+1))-ABS(SLLP) ADDSED=ABS(ADDSED) DEP(IJ,J+1)=SLLP 76 X(IJ)=IJ DD{IJ)=DEP(IJ,J+1)*-1. 74 CONTINUE IF(ADDSED.LE.O.O) GOTO 898 JN=0 DO 746 IJ=NK1+1,NK2 JN=JN+1 SEDDEP=(ADDSED\7)*((1 -.7)**(JN-1 )) DEP(!J,J+1 )=DEP(IJ,J)-SEDDEP CALF=DEP(IJ,J+1)-SLLP IF(CALF.GT.O.O) GOTO 769 ADDSED=ABS(DEP(IJ,J+1))-ABS(SLLP) ADDSED=ABS(ADDSED) DEP(IJ,J+1)=SLLP 769 X{IJ)=IJ DD(IJ)=DEP(IJ,J+1)*-1. 746 CONTINUE

898 CONTINUE

C CHECK TO SEE IF A STORM OCCURRED

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 280

CALL SAM(PR0BD,1 .IDUM.PARM1 .PARM2.ZSAMPLE) Z2SAMPLE(J)=ZSAMPLE 1F(Z2SAMPLE(J).GT.0.95) GOTO 500

JN=0 DO 80 JI=NK1,NCELS JN=JN+1 DEP(JI,J+1 )=DEP(J!.J)-SMUD 80 CONTINUE

GOTO 1001

C IF A STORM OCCURED HOW INTENSE WAS IT ?

500 CALL SAM(PR0BD,1,IDUM,PARMI ,PARM2,ZSAMPLE) Z3SAMPLE(J)=2SAMPLE C WRITE(6.333) J 333 FüRMAT(1X,'STORM OCCURED AFTER ',16,' YEARS')

IF(Z3SAMPLE(J).LE.0.75) SST=0.20

IF(Z3SAMPLE(J).GT.0.75.AND.Z3SAMPLE(J).LE.0.95) SST=0.30

IF(Z3SAMPLE(J).GT.0.95) SST=0.40 w ss=ssrio. C WRITE(7,*) J.WSS 332 F0RMAT(1 X,'STORM INTENSITY = ',F4.1.' (MAX = 1 )')

JN=0 NKK=NK2-NK1 PK=1.-((0.01)**(1./(NKK+1)))

DO 90 JI=NK1,NCELS JN=JN+1

SST=SST-0.02 IF(SST.LT.O) SST=0.0 DEP(JI,J+1 )=DEP(JI,J)-ABS(SST) IF(JI.LT.NK2) GOTO 90 DEP(JI,J+1 )=DEP(JI,J+1 )-SMUD 90 CONTINUE

C JN=0 C DO 701 JI=NK2,NCELS C JN=JN+1

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 281 C DEP(JI,J+1)=DEP(JI,J)-SMUD c 701 CONTINUE

1001 CONTINUE

C... MAKE CORRECTION FOR EUSTATIC SEA-LEVEL CHANGE AND UNIFORM SUB

10041 SLCJ=SLC(J+11-SLC(J) IF(SLQU.EQ.O) GOTO 10032 SLCJ=SLC(1) 10032 CONTINUE SUB=RSS DO 119 Jl=1,NCELS DEP(JI,J+1)=DEP(JI.J+1)+SUB IF(SLCJ.LT.O.) GOTO 129 DEP(JI,J+1 )=DEP(JI,J+1 )+SLCJ GOTO 119 129 DEP(JI,J+1 )=DEP(JI,J+1 )-ABS(SLCJ) 119 CONTINUÉ

IF(MORESUB.EQ.O) GOTO 100 C MAKE LOCALISED SUBSIDENCE CALCULATIONS ASUB=GFSUB JN=0 DO 159 IJ=ICEL,KCEL JN=JN+1 DEP(IJ,J+1 )=DEP(IJ,J+1 )+(ASUB) ASUB=ASUB-(ASUB/10.) IF(ASUB.LT.O.) ASUB=0. 159 CONTINUE

1009 CONTINUE 100 CONTINUE SLLP=SLLP-SL

8888 CONTINUE IF(PLRQ.EQ.O) GOTO 122 DO 895 IK=1,NTIME NSH=NSHOR(IK) NTT=100-NSH C WRITE(7,*) NSH.NCELS DO 896 KI=NSH,NCELS DD(KI)=DEP(KI,IKr(-1) X(KI)=KI C WRITE(7,*) X(KI),DD(KI) 896 CONTINUE CALL FRSTW(X(NSH).DD(NSH))

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 282 CALL CURVEW(X,DD,NTT) 895 CONTINUE 122 CONTINUE

C...... END OF MAIN LOOP

C CALL SORT(SAMPLE,NTIME) C WRITE(7,*)(SAMPLE(M).M=1,100) C CALL EQWID(SAMPLE.NTIME,50.FREQ,UB,RMIN,RMAX) C WRITE(7,*)(FREQ(KM) ,KM=1,50)

C DO 200 J=1,100 C WRITE(7,31) X(J).(DEP{J,M),M=1,1000,100)

0 200 CONTINUE 14 FORMAT(/////////////////////,30X,’D E P S I M7/. +13X,'A program to simulate shoreface progradation under variable', +/,17x,’sea-level sediment supply and subsidence conditions.') 19 FORMAT(///,36x,'Written by',//,35x,'Philip Lowry'/// +,34x,'Dept of Geology',/,28x,'Louisiana State University',//) 31 FORMAT(1X,F4.0.10F7.2) 101 FORMATC SED SUPPLY SWITCHED AT ',15.' YEARS SED SUPPLY = ', FI 2.2) 300 FORMAT(10X,2F16.6) 301 F0RMAT(1X,’********"*"*******’‘************‘******‘ *******‘ '^^'',//, +' NORMAL DISTRIBUTION MEAN = ',F8.2,' ST. DEV. = ',F8.2,//, + * * ) CALL FRAME STOP END

c C*** FAST ASCENDING SORT ROUTINE C - c c SUBROUTINE SORT(A.N) DIMENSION A(N) M2=2*N-1 5 M2=INT(M2/2) IF(M2.EQ.0)GOTO10 K=N-M2

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 283 DO 201=1 ,K DO 30 J2=1.I,M2 N2=I-(J2-1) L2=N2+M2 IF(A(L2).GT.A(N2)) GOTO 20 B2=A(N2) A(N2)=A(L2) A(L2)=B2 30 CONTINUE 20 CONTINUE GOTO 5 10 CONTINUE RETURN END C c C*** SAMPLING ROUTINE C

SUBROUTINE SAM(TYPE,SIZE,ISEED,PARMI .PARM2,SAMPLE) INTEGER TYPE,SIZE REAL MU,MAX,MIN,SAMPLE(SIZE) IF(TYPE.EQ.1)THEN 'UNIFORM DIST. MAX=PARM2 MIN=PARM1 RANGE=MAX-MIN DO 10 1=1,SIZE R1=RAN(ISEED) IF(R1 .EQ.0.0)R1 =RAN(ISEED) SAMPLE(I)=(R1 *RANGE)+MIN 10 CONTINUE C ELSE IF(TYPE.EQ.2)THEN INORMAL DIST. MEAN MU, SD SIGMA MU=PARM1 SIGMA=PARM2 MAX=MU+4.0*SIGMA MIN=MU-4.0*SIGMA DO 20 1=1 .SIZE 40 IF(Z.EQ.1.00) GO TO 30 Z=1.00 R1=RAN(ISEED) IF(R1 .EQ.0.0)R1 =RAN(ISEED) R2=RAN(ISEED) IF(R2.EQ.0.0)R2=RAN(ISEED) Z1=SQRT(-2.0*ALOG(R1)) Z2=6.28319*(R2) SAMPLE(l)=ZrSIN(Z2)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 284 GOTO 50 30 Z=0.0 SAMPLE(l)=ZrC0S(Z2) 50 SAMPLE(I)=SIGMA*SAMPLE(I)+MU IF(SAMPLE(I).LT.O.O) GOTO 40 IF(SAMPLE(l).GE.MAX)GOTO 40 IF(SAMPLE(l).LT.MIN)GOTO 40 20 CONTINUE ENDIF RETURN END G

0 0** ROUTINE TO FORM EQUAL WIDTH CELLS C ...... c SUBROUTINE EQWID(SAMPLE,SIZE,K,FREQ,UB)

INTEGER SIZE

REALSAMPLE(S1ZE),FREQ(K),UB(K),MIN,MAX MIN=0.0 MAX=1.0 RANGE=MAX-MIN L=1 WIDTH=RANGE/K DO10l=1,K FREQ(l)=0.0 UB(I)=MIN+(I*WIDTH) 200 IF(LLE.SIZE)THEN IF(SAMPLE(L).GT.(UB(1)+.00001 ))GOTO 10 FREQ(I)=FREQ(I)+1 L=L+1 GOTO 200 ENDIF 10 CONTINUE RETURN END Q...... C ...... c C HISTOGRAM ROUTINE *** Q...... C c SUBROUTINE HIST(MARKS,CMARKS,NCLASS) REAL MARKS(NCLASS),CMARKS(NCLASS)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 285 INTEGER LINE(24) DATA LINE/24*1 H /.IAST/1 HV.IBLA/1 H / □ 0 51=1,50 J=51-l D0 4K=1,NCLASS IMARK=INT(MARKS(K))/2 IF(IMARK.GE.J)LINE(K)=IAST 4 CONTINUE 1F(MOD(J.5).NE.O.O) THEN WRITE(6.S)((LINE(K),L=1,3).K=1 .NOLASS) 8 F0RMAT(4X,1 HI,24(2X,3A1 )) ELSE WR!TE(6,9)J*2,((LINE(K),L=1,3),K=1,NOLASS) 9 F0RMAT(1 X,I2,2H +,24(2X,3A1 )) ENDIF 5 CONTINUE LAST=NCLASS IF(MOD(NCLASS,2).NE.O.O)LAST=NCLASS-1 WRITE(6,11 )(CMARKS(I),I=2,UST,2) 11 FORMAT(4X.1H+.24(5H—+-),2H-/5X,12F10.1///) □ 0 61=1,24 LINE(I)=IBLA 6 CONTINUE RETURN END C C SUBROUTINE EQWID2(SAMPLE,ISIZE,WIDTH,RMIN,RMAX,FREQ,CMARKS,UB) REALSAMPLE{IS1ZE),FREQ(40),CMARKS(20),UB(20) DO5KK=1,40 FREQ(KK)=0.0 5 CONTINUE RANGE=RMAX-RMIN L=1 NCLASS=INT(RANG&WIDTH)+1 DO 10 l=1,NCLASS UB(I)=RMIN+(I*WIDTH) CMARKS(I)=UB(I)-(0.5*W1DTH) IF(LGT.ISIZE)GOTO10 200 IF(SAMPLE(L).GE.UB{l))GOTO10 FREQ(I)=FREQ(I)+1 L=L+1 IF(LGT.ISIZE)GOTO10 GOTO 200 10 CONTINUE WIDTH=FLOAT(NCLASS) RETURN END

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 286 C

SUBROUTINE SETUP([.J,K,S,T.M1 ,M2,L.M) LOGICAL FIRST

DATA FIRST/.TRUE./

C IF(FIRST)0PEN(10,FILE='START.DAT) READ(10,1 OO.END=99)I.J.K.S,T,M1 ,M2,L,M 100 F0RMAT(3I5.2F12.6,415) FIRST=.FALSE. RETURN 99 STOP’NO INPUT END

SUBROUTINE CHECK2(FREQ.NCLASS,ISIZE) REAL FREQ(NCLASS) ISUM=0 DO 10 J=1,NOLASS ISUM=ISUM+FREQ(J) 10 CONTINUE IF{ISUM.NE.ISIZE)WRITE(6,100)ISUM,ISIZE 100 FORMAT(2I10) RETURN END

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 287

PROGRAM STRATSIM C C A PROGRAM TO SIMULATE THE DEVELOPMENT OF SEQUENCE C BOUNDARIES AND SHORELINE SHIFTS IN RESPONSE TO BASIN 0 SUBSIDENCE AND SEA-LEVEL FLUCTUATIONS. SEA-LEVEL C FLUCTUATIONS MAY BE EITHER CYCLIC (VAIL) C OR VARIABLE RATES OF FALL (PITMAN). THE ALGORITHMS USED IN C THIS PROGRAM ARE BASED ON THOSE IN PITMAN (1978) C C WRITTEN BY C C PHILIP LOWRY C DEPT. OF GEOLOGY C LOUISIANA STATE UNIV. C BATON ROUGE, LA 70803-4101 C

C D = DISTANCE TO SHELF BREAK C RSS = RATE OF SUBSIDENCE AT SHELF BREAK C RSL = RATE OF SEA LEVEL CHANGE (CM/1000 YR) C XL = DISTANCE OF SHORELINE FROM HINGLINE (CM) C X = DISTANCE OF ANY POINT ON SHELF FROM HINGELINE (CM) C XLI = POSITION OF SHORELINE AFTER PREVIOUS CALCULATION C SL = SLOPE OF SHELF (RADIANS) C

DIMENSION X(310),Y(300,300),XLI(10000),SED(1000),RSL(100000) DIMENSION DD(101 ),SLAMP(5),SLWVL(5),SLC(10001 ),SLP(10001 ) DIMENSION Y1(300) INTEGER PROBD.PLRQ DATA PI/3.141592654/ 0PEN(UNIT=7,FILE='SIM.DAT,STATUS='NEW)

WRITE(6,10) 10 FORMAT(///25X,’ STRATS I M7/, 1 SX.’A program to simulate' + ' deposltional sequences',//35x,'by'//29x,'Philip Lowry') WRITE(6,20) 20 F0RMAT(////,1 Ox,' Enter sedimentation rate (cm/1000 yr)') READ(5,*) SR WRITE(7,*) SR SR=SR/1000. 777 WRITE(6,21) 21 F0RMAT(//,1 OX,' Enter the limits of the plot section') READ(5,*) XL,XM,YL,YM WRITE(6,223) 223 FORMAT(//,10X,' Enter the number of sequences to be simulated') READ(5,*) NS

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 288 WRITE(6,2615) 2615 FORMAT(//,1 Ox,'Enter the duration of a sequence’) READ(5*)T WRITE(6.2003) 2003 FORMAT(1X,'Do you want a plot of the sea-level curve?') READ(5,*) QUES WRITE(6.881) 881 F0RMAT(1x,'Enter 5 sea-level cycle wavelengths and amplitides') D0 769J=1,5 READ{5,*) SLWVL(J),SLAMP(J) WRITE(7/) SLWVL(J),SLAMP(J) 769 CONTINUE WR1TE{6.456) 455 FORÎ^AT(1X,'Hûw many sea-level cycles should be used?') READ(5,*) NSC

C CONSTANT INPUT DATA C 0=25000000 RSS=0.0025 XLI(1)=0. SL=0.0002 N T = rN S NP=100000 ND=D K1=1 ND2=ND/100000 NP2=NP/100000 NP3=D/NP

WRITE{6,8795) 8795 F0RMAT(1x,'Use Pitmans sea-level data? (1=Yes/0=No)') READ(5,*) APD IF(APD.EQ.O.) GOTO 1765 DO 848 IL=1,NS WRITE(6,847)IL 847 F0RMAT(1X,'Enter sea-level fall for sequence ',13) READ(5,*) RSL(IL) 848 CONTINUE

C FOR SEA LEVEL FALL DATA BETWEEN 65-15 MA SEE PITMAN, 1978. C CONVERT TO CMTfR C GOTO 983

C...... DEFINE THE SEA LEVEL CURVE 1765 JN=0 PII=PI/2

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 289 NITS=1 DO 360 U=1,NT.T JN=JN+1 ASL=0. DO 120 KKJ =1,NSC CON=PII ASL=ASL+SLAMP(KKJ)*(S1N((2*P1*LJ)/(SLWVL(KKJ))+C0N)) 120 CONTINUE SLC(JN)=ASL SLP(JN}=JN 360 CONTINUE JN=0 DO 973 KNN=T,NT,T JN=JN+1 RSUJN)=(SLC(JN+1 )-SLC(JN))/T RSL(JN)=RSL(JN)*(-100.) WR!TE(6,*) RSL(JN).SLC(JN),JN 973 CONTINUE JSN=JN

C C SET UP INITIAL SLOPE PROFILE C 903 KN=0 DO 60 K=0,ND2,NP2 KN=KN+1 X(KN)=K Y(KN.1)= (K *S L r-1 Y{KN,1)=Y(KN.iri000. C WRITE(6,*)Y(KN,1) 60 CONTINUE

C BEGIN LOOP FOR EACH INTERVAL OF TIME. COMPUTE CONSTANTS C DO 30 K=T,NT,T C K1=K1+1 C1=(D*SURSS) C2=RSL(K1-1)+SR C3=((XLI(K1-1)rRSS)/D C4=(rRSS)/(D*SL) C5=(RSL(K1 -1 r(D/RSS))+(SR*{D/RSS)) SLLC=RSL(K1-1) c WRITE(7,100) 100 F0RMAT(//9X,’DIST (KM) SUBSID (M) SED (M) TOTAL (M)') C C BEGIN LOOP FOR EACH LOCATION ON THE PROFILE C

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 290 J=0 DO 40 l=0,ND.NP J=J+1 c C6=RSS*T C6=(I*RSS)*(T/D) C C COMPUTE SEDIMENTATION AT LOCATION J C SED(J)={C6-(RSL(KM )*T))-(C1*(C2-C3)*((EXP(-C4))-1 )) SED(J)=SED(J)/100. C6=C6/100.

Y(J,K1)=Y(J.K1-1)+SED(J) C C C SUBSIDE PREVIOUS SHELF PROFILE THEN ACCOUNT FOR SEA LEVEL C CHANGE C7=(SLLC*T)/100. NN=K1+1 DO 66 N=2,NN

Y(J,N-1)=Y(J,N-1)+C7-C6 66 CONTINUE SUM=C6+SED(J) c WRITE(7,500) J.C6,SED(J),SUM 500 F0RMAT(5X,I8.3E16.4) 40 CONTINUE C C COMPUTE NEW SHORELINE POSITION C XLI(K1 )=C5-((EXP(-C4))*(C5-XLI(K1 -1 ))) c XLI(K1)=XLI(K1)/100000. WRITE(7,300) K. XLI(K1) 300 F0RMAT(1 X,.'SHORELINE AFTER '.19,' YEARS = '.El 2.4,' KM') 30 CONTINUE C C FIND MAX AND MIN VALUES c NP9=NP3-1 C IF(YL.EQ.YM) GOTO 900 XMIN=XL XMAX=XM YMIN=YL YMAX=YM GOTO 800 900 XMIN=X(1) XMAX=XMIN

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 291 YMIN=Y(1,1) YMAX=YMIN DO 2000 JJ=1 ,K1 DO 1000 l=1,NP3 C IF(JJ.GT.I) GOTO 1001 IF(X(I).LT.XMIN) XM1N=X(1) IF(X(I).GT.XMAX) XMAX=X(I) 1001 IF(Y(I,JJ).LT.YMIN) YMIN=Y(I,JJ) IF(Y(I.JJ).GT.YMAX) YMAX=Y(I,JJ) 1000 CONTINUE 2000 CONTINUE C 0 SET UP THE PLOTTING ROUTINES 800 YY=(YMIN-YMAX)/2 XX=(XMAX-XMIN)/2 Y2=YMAX+ABS(YMIN/10) X2=XMIN-XMAX/20 Y3=YMIN-ABS(YMIN/10) X3=XMIN+XMAX/10 X4=XMIN-XMAX/10 0 CALL SET(0.2..8,0.2..8,XMIN,XMAX,YMIN,YMAX,1 ) CALL LABM0D(7H(F10.0),7H(F10.0),10.10.0,0,10.-30.0) CALL HALFAX(5.0.12,0,XMIN,YMAX,1.1 ) CALL PWRIT(XX,Y2. ’DISTANCE (KM)’,13,1,0,-i) CALL PWRIT(X4.YY. 'DEPTH (M)',8.1.90,-1) CALL PWRIT(X3,Y3, 'SEQUENCE BOUNDARIES (85-15 MA)'.30.3.0.-1)

C PLOT THE SHELF PROFILE C DO 70 11= 1 ,K1 NC=0 DO 90 IJ=1,NP3 C WRITE(7,*) X(!J),Y(IJ,1I) c WRITE(7,232) X(IJ),Y(IJ,II) 232 FORMAT(5X,2E15.3) C IF(IJ.GT.I) GOTO 920 IF(X(IJ).GT.XMAX) GOTO 90 IF(X(IJ).LT.XMIN) GOTO 90 IF(Y(IJ,II).LT.YMIN) GOTO 90 IF(Y(IJ,II).GT.YMAX) Y(IJ,ll)=0. NC=NC+1 X(NC)=X(IJ) Y1(NC)=Y(IJ,II) IF(Y1(NC).GT.0.)Y1(NC)=0. 90 CONTINUE IF(NC.EQ.O) GOTO 77 CALL FRSTPT(X(1),Y1(1)) CALL CURVE(X,Y1.NC)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 292 70 CONTINUE 0 C CALL FRAME IF(QUES.EQ.O) GOTO 2765 CALL EZXY(SLP,SLC,JSN,’SEA LEVEL CURVES') 2765 CONTINUE

GOTO 888 77 WRITE(6,78) 78 F0RMAT(//,5X/ BAD PLOTTING WINDOW! EXTEND LIMITS’) GOTO 777 888 CALL FRAME STOP END

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX

POROSITY, PERMEABILITY, OIL AND WATER SATURATION DATA FROM CORE PLUGS AND SIDEWALL SAMPLES LOCKHART CROSSING FIELD

293

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 294

Gallon Petroleum, State Lease 7729 #2

K(md)xlQ Sq(%) 0 10 20 30 40 50 60 20 40 60 80 100 10,140 —I------1------1------r T

Permeability (k) Porosity (0)

10,160

10,180

10,200

10,220 100 80 60 40 20 0 Sw (%)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 295

JS.HOWELL

K(md) S q(%) 0 20 40 60 80 100 120 0 20 40 60 80 100 10,340 “I 1------1------1------1------1—

Permeability (k) Porosity (0)

10,360

10,380

10,400 -

10,420 ■ 10 20 30 100 80 60 40 20 0 0(%) Sw (%)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 296

HOWELL 364

K(md)xlO SqW 0 15 30 45 60 75 90 10,340 1 ------1------1------0 20 40 60 80 100 T T T T T Permeability (k) [ ] sw Porosity (0)

10,360 -

10,380 i

10,400 -

10,420 _L _L 10 20 30 100 80 60 40 20 0(%) Sw (%)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 297

GEORGIA PACIFIC #1 K(md)xlO SoMW 30 60 90 120 150 180 40 60 80 100 10,170 —r- —T T T

Permeability (k) Porosity (0)

10,190 À

10,210

0 0 0

10,230

10,250 J_ _L 10 20 30 100 80 0(%)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 298

CROWN ZELLERBACH #3

K ( m d ) x l O Sq(%) 0 20 40 60 '60 100 120 0 20 40 60 80 100 —r ~r T ~r TT Permeability (k) Porosity (0)

_L I _L 10 20 30 100 80 60 40 20 0(%) S y/ (%)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 299

A. THOM #3

K ( m d ) x l O So(%) 0 20 40 60 80 100 120 20 40 60 80 100 10,190

Permeability (k) jS ill Porosity (0)

10.210

10,230

10,250 -

10,270 ■ 10 20 30 100 80 60 40 20 0 0(%) Sw (%)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 300

GAUGIN et al K(md) SoMO 20 30 40 50 60 20 40 60 80 100 10290 T

Permeability (k) *w Porosity (0)

10300 -

10,310

«MM 10,320

«SB

10,330 100 80 60 40 Sw (%)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 301

J.W BENNET

K(md)xlO S q(%) 60 90 120 ISO 180 10,220 40 60 80 100 “ 1 r T T T Permeability (k) ’W Porosity (0)

10 ,2 4 0

1 0 ,2 6 0

1 0 ,2 8 0 -

1 0 ,3 0 0 ■ _L J_ 10 20 3 0 1 00 80 6 0 4 0 20 0(%) Sw (%)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 302 DEPTH PERMEABILITYPOROSITY OIL % WATER %

CROWN ZELLERBACH#1 10170.00 76.00 20.90 12.80 43.60 10171.00 77.00 20.20 15.70 48.20 10172.00 72.00 20.40 13.40 43.30 10173.00 62.00 21.50 11.40 49.10 10174.00 33.00 19.80 10.80 40.60 10175.00 83.00 21.70 21.80 38.20 10176.00 14.00 17.80 11.60 41.90 10177.00 53.00 20.00 16.40 35.50 10178.00 39.00 20.60 13.20 47.10 10179.00 55.00 19.40 10.90 56.50 10180.00 27.00 18.60 8.70 50.50 10181.00 24.00 17.60 9.30 53.30 10182.00 32.00 19.20 12.80 31.20 10183.00 35.00 19.50 7.10 45.10 10184.00 48.00 20.60 11.20 43.00 10185.00 39.00 21.70 10.40 40.00 10186.00 40.00 21.20 10.50 38.40 10187.00 18.00 18.90 7.90 44.60 10188.00 49.00 20.90 9.30 46.00 10189.00 34.00 20.60 6.60 48.30 10190.00 31.00 19.80 9.30 54.80 10191.00 32.00 20.10 10.00 52.90 10192.00 18.00 19.30 4.90 54.10 10193.00 40.00 20.00 8.40 50.40 10194.00 78.00 20.20 9.50 45.20 10195.00 130.00 21.20 12.70 45.10 10196.00 14.00 18.70 0.00 62.30 10197.00 0.27 10.90 0.00 56.00 10198.00 28.00 20.20 0.60 68.30 10199.00 14.00 20.20 O.'.O 66.70 10200.00 55.00 21.40 3.10 52.20 10201.00 9.40 19.40 0.60 66.90 10202.00 14.00 20.50 0.00 62.10 10203.00 11.00 19.70 0.00 61.60 10204.00 12.00 20.50 0.00 62.50 10205.00 13.00 20.30 0.00 53.20 10206.00 12.00 20.60 0.00 53.20 10207.00 11.00 20.60 0.00 59.20 10208.00 13.00 21.30 0.80 53.40 10209.00 11.00 21.10 0.70 59.10 10210.00 2.40 17.50 0.00 57.60

GEORGIA PACIFIC #1 10191.00 115.00 22.30 9.40 43.20 10192.00 100.00 23.20 7.90 48.40 10193.00 50.00 18.80 9.60 42.30 10194.00 79.00 21.60 11.10 48.10 10195.00 66.00 18.80 7.20 44.90

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 303 10196.00 44.00 21.70 10.10 40.50 10197.00 39.00 20.50 3.70 51.90 10198.00 54.00 21.30 0.00 54.60 10199.00 50.00 19.60 0.00 62.70 10200.00 80.00 20.50 0.00 74.60 10201.00 36.00 20.70 0.00 56.10 10202.00 42.00 21.20 0.00 68.70 10203.00 35.00 21.10 0.00 56.30 10204.00 29.00 20.00 0.00 60.50 10205.00 34.00 20.40 2.60 57.60 10206.00 31.00 21.20 0.00 58.20 10207.00 12.00 20.00 0.00 61.70 10208.00 33.00 17.20 0.00 59.50 10209.00 23.00 18.70 0.00 63.40 10210.00 19.00 18.60 0.00 65.20 10211.00 28.00 17.90 0.00 60.00 10212.00 33.00 19.70 0.00 62.60 10213.00 29.00 20.70 0.00 59.30 10214.00 31.00 20.00 0.00 62.80 10215.00 125.00 22.70 0.00 60.20 10216.00 98.00 22.90 0.00 70.60 10217.00 10.00 17.90 0.00 58.60 10218.00 1.29 12.60 0.00 65.10 10219.00 29.00 21.20 0.00 60.30 10220.00 19.00 20.20 0.00 55.60 10221.00 32.00 22.10 0.00 60.50 10222.00 12.00 20.20 0.00 69.20 10223.00 19.00 20.90 0.00 60.60 10224.00 7.65 18.40 0.00 67.00 10225.00 11.00 20.30 0.00 61.70 10226.00 9.97 19.40 0.80 59.50 10227.00 7.03 19.30 0.00 68.90 10228.00 13.00 19.50 0.00 72.50 10229.00 6.05 18.00 0.00 64.60 10230.00 12.00 18.90 0.00 63.50 10231.00 13.00 19.90 0.90 72.10 10232.00 9.41 19.20 0.00 68.60 10233.00 3.00 17.20 0.00 73.70 AMOCO IPCO #1 10173.00 13.00 11.20 0.00 61.00 10174.00 37.00 21.10 28.90 37.70 10175.00 46.00 20.70 15.00 45.00 10176.00 82.00 19.70 14.20 44.20 10177.00 57.00 22.30 13.10 48.90 10178.00 38.00 22.30 11.70 50.50 10179.00 45.00 23.20 13.30 48.90 10180.00 36.00 22.20 12.10 49.30 10181.00 49.00 21.60 13.50 41.90 10182.00 40.00 19.40 14.20 39.60 10183.00 42.00 23.40 12.30 47.90

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o CO

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"O 8 3 1 Q. S: 305 10239.00 16.00 20.70 17.90 48.20 10240.00 37.00 21.60 14.80 49.30 10241.00 36.00 21.80 12.40 48.50 10242.00 87.00 23.20 12.10 47.70 10243.00 39.00 22.40 14.30 49.80 10244.00 77.00 22.90 15.30 48.20 10245.00 82.00 23.50 13.20 50.10 10246.00 116.00 24.20 11.60 52.70 10247.00 13.00 19.90 10.20 54.60 10248.00 18.00 20.40 8.80 58.80 10249.00 17.00 20.00 8.00 67.20 10250.00 12.00 18.60 6.50 70.10 10251.00 18.00 19.10 5.20 72.30 10252.00 14.00 17.80 8.40 69.10 10252.50 13.00 17.20 0.00 82.80 10253.00 15.00 17.50 0.00 81.90 10254.00 16.00 18.30 4.90 78.20 10255.00 13.00 18.00 0.00 82.20 10256.00 8.50 16.90 0.00 84.00 10257.00 30.00 20.20 0.00 83.70 10258.00 15.00 19.50 0.00 83.60 10259.00 9.20 17.30 0.00 84.20 10260.00 10.10 18.00 0.00 84.80 10261.00 12.00 18.30 0.00 83.90 10262.00 21.00 19.80 0.00 82.20 10263.00 8.70 17.20 0.00 81.90 10264.00 6.50 16.60 0.00 81.70 10265.00 3.30 16.20 0.00 82.20 10265.50

GALLON MAGGIE C0LL1NS#1 10205.00 13.00 21.00 0.00 80.30 10206.00 58.00 21.60 0.00 81.40 10207.00 60.00 22.20 0.00 81.20 10208.00 69.00 21.90 0.00 78.90 10209.00 61.00 20.10 0.00 82.60 10210.00 34.00 20.40 0.00 78.40 10211.00 29.00 21.90 0.00 79.10 10212.00 38.00 19.40 0.00 76.40 10213.00 52.00 21.50 0.00 77.00 10214.00 37.00 19.60 0.00 79.50 10215.00 22.00 21.10 0.00 79.10 10216.00 49.00 20.80 0.00 77.60 10217.00 52.00 21.20 0.00 80.00 10218.00 25.00 21.30 0.00 81.40 10219.00 20.00 19.30 0.00 75.10 10220.00 17.00 20.40 0.00 77.90 10221.00 29.00 21.60 0.00 78.40 10222.00 30.00 21.20 0.00 80.50 10223.00 20.00 20.50 0.00 78.30 10224.00 12.00 20.80 0.00 79.20

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 306 10225.00 22.00 19.90 0.00 79.50 10226.00 23.00 20.60 0.00 77.40 10227.00 21.00 20.40 0.00 76.80 10228.00 20.00 19.70 0.00 76.30 10229.00 22.00 20.50 0.00 76.00 10230.00 11.30 17.40 0.00 81.60 10231.00 17.00 20.60 0.00 82.00 10232.00 13.00 17.70 0.00 78.00 10233.00 15.00 17.20 0.00 86.10 10234.00 21.00 22.30 0.00 78.50 10235.00 84.00 22.00 0.00 79.10 10236.00 4.50 16.30 0.00 82.80 10237.00 12.00 17.50 0.00 81.50 10238.00 4.70 17.80 0.00 84.60 10239.00 8.00 18.30 0.00 82.20 1C 240.00 5.70 17.90 0.00 83.50 10241.00 6.10 18.00 0.00 86.10 10242.00 5.70 18.40 0.00 84.20 10243.00 6.50 18.60 0.00 83.60 10244.00 12.00 18.50 0.00 87.10 10245.00 5.20 17.30 0.00 82.20 10246.00 11.00 16.90 0.00 81.90 10247.00 1.60 15.40 0.00 86.30 BARNETT #2 10158.00 105.00 21.30 14.90 39.90 10159.00 68.00 19.60 12.50 44.20 10160.00 110.00 20.00 12.80 34.90 10161.00 69.00 23.20 10.80 36.70 10162.00 6.10 12.30 7.90 51.70 10163.00 150.00 20.40 10.50 37.10 10164.00 33.00 17.60 9.30 45.40 10165.00 42.00 19.50 8.40 45.80 10166.00 51.00 18.90 17.80 30.10 10167.00 14.00 14.60 ■ 14.60 43.70 10168.00 13.00 16.40 9.40 52.70 10169.00 305.00 22.90 13.30 37.80 10170.00 230.00 22.00 17.00 37.70 10171.00 78.00 18.80 14.30 28.60 10172.00 220.00 22.80 11.50 35.10 10173.00 500.00 23.90 10.70 35.20 10174.00 700.00 24.30 11.00 41.10 10175.00 595.00 24.00 14.40 33.30 10176.00 15.00 13.70 10.60 52.10 10177.00 17.00 14.00 13.00 44.40 10178.00 0.47 11.40 5.00 63.30 10179.00 21.00 17.20 10.30 38.50 10180.00 390.00 23.00 14.60 35.90 10181.00 0.14 9.60 9.30 61.90 10182.00 110.00 19.20 14.40 41.10 10183.00 0.37 14.50 7.10 35.70 10184.00 75.00 20.80 10.10 49.30

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 307 10185.00 5.40 15.70 6.30 57.70 10186.00 315.00 23.00 16.00 37.00 10187.00 2.40 14.00 16.30 51.20 10188.00 16.00 14.00 9.30 66.70 10189.00 37.00 17.80 13.00 41.60 10190.00 0.37 12.30 5.40 64.90 10191.00 39.00 15.20 7.10 60.60 10192.00 55.00 17.60 8.30 56.50 10193.00 3.20 13.70 9.70 47.30 10194.00 12.00 15.00 8.80 43.90 10195.00 505.00 24.20 12.10 32.70 10196.00 475.00 23.30 15.60 31.20 10197.00 9.10 14.30 12.50 37.50 10198.00 0.38 11.50 8.30 55.00 10199.00 57.00 19.30 12.40 47.60 10200.00 125.00 21.10 16.10 32.30 10201.00 14.00 15.10 7.30 64.40 10202.00 25.00 15.00 8.90 38.00 10203.00 20.00 16.20 11.50 29.50 10204.00 25.00 14.60 6.00 71.80 10205.00 37.00 16.70 8.40 36.90 10206.00 24.00 15.70 7.70 54.70 10207.00 9.70 15.20 8.30 55.00 10208.00 115.00 21.30 11.30 39.10 10209.00 150.00 22.60 13.00 53.80 10210.00 99.00 21.00 9.60 39.00 10211.00 190.00 23.40 12.00 42.30 10212.00 215.00 23.70 16.40 38.50 10213.00 155.00 23.10 9.00 28.50 10214.00 150.00 21.90 8.70 44.60 10215.00 245.00 23.80 9.30 36.30 10216.00 180.00 23.30 13.20 30.90 10217.00 230.00 24.00 13.20 32.20 10218.00 120.00 22.90 11.50 41.60 10219.00 94.00 20.10 9.10 46.60 10220.00 260.00 22.50 9.70 38.00 10221.00 140.00 22.70 13.40 42.30 10222.00 0.03 8.40 0.00 85.40 10223.00 0.05 7.80 2.80 78.70 10224.00 0.55 4.20 2.50 87.70 W. LEONARD #1 10666.00 0.80 17.50 0.00 73.90 10667.00 16.00 17.10 0.00 67.70 10668.00 38.00 18.10 0.00 69.00 10669.00 0.13 14.00 0.00 75.00 10670.00 0.01 4.00 0.00 81.50 10671.00 0.01 4.20 0.00 90.30 10672.00 0.01 5.50 0.00 88.90 10673.00 0.01 5.40 0.00 78.60 10674.00 0.01 3.40 0.00 86.20

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 308 10675.00 0.01 4.00 0.00 90.00 10676.00 0.01 3.90 0.00 86.40 10677.00 0.01 3.30 0.00 88.90 10678.00 0.01 4.40 0.00 90.30 10679.00 0.01 5.00 0.00 89.50 10680.00 0.01 6.60 0.00 93.60

STATE LEASE 7729#1 10105.00 672.00 23.80 1.40 67.40 10106.00 1770.00 26.10 0.90 63.70 10107.00 1822.00 28.50 0.00 59.00 10108.00 696.00 27.60 0.00 60.60 10109.00 1556.00 24.30 0.00 54.00 10109.50 10110.00 10111.00 10112.00 0.28 15.40 0.00 74.60 10113.00 0.07 13.00 0.00 82.40 10114.00 10114.50 0.20 13.90 0.00 80.80 10115.00 10116.00 10117.00 10118.00 0.33 12.20 0.00 68.40 10119.30 0.25 15.50 0.00 82.40

GALLON CZ #5 10171.00 79.00 22.30 11.60 37.40 10172.00 44.00 22.60 12.40 37.20 10173.00 81.00 21.10 11.10 37.60 10174.00 73.00 21.40 7.20 38.60 10175.00 49.00 22.50 11.80 38.20 10176.00 50.00 21.30 7.80 38.00 10177.00 48.00 22.00 10.30 38.10 10178.00 134.00 23.80 13.20 32.20 10179.00 69.00 22.20 11.00 36.00 10180.00 48.00 21.90 10.00 32.30 10181.00 49.00 19.40 9.70 46.60 10182.00 61.00 22.80 10.90 34.80 10183.00 34.00 22.00 8-40 38.50 10184.00 49.00 23.70 10.10 33.70 10185.00 24.00 22.60 8.60 34.30 10186.00 50.00 22.60 8.00 38.40 10187.00 48.00 21.90 8.80 43.40 10188.00 39.00 24.60 10.00 40.00 10189.00 50.00 23.60 7.60 40.30 10190.00 35.00 21.50 8.20 28.40 10191.00 27.00 18.70 7.60 52.20 10192.00 26.00 19.40 8.80 32.20 10193.00 26.00 21.20 5.70 46.50 10194.00 30.00 23.50 6.50 41.90

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 309 10195.00 34.00 23.30 9.50 39.90 10196.00 119.00 23.60 12.70 30.90 10197.00 108.00 21.00 11.80 29.40 10198.00 12.00 20.80 0.00 46.20 10199.00 15.00 22.20 1.80 40.90 10200.00 98.00 26.00 1.10 50.10 10201.00 105.00 27.30 12.20 31.00 10202.00 21.00 23.90 7.10 38.30 10203.00 20.00 24.00 1.00 46.00 10204.00 2.30 12.80 0.00 42.30 10205.00 0.08 10.90 0.00 53.30 10206.00 7.91 19.90 0.00 50.00 10207.00 11.00 20.20 0.00 51.50 10208.00 8.26 19.20 0.00 55.70 10209.00 12.00 20.90 0.00 50.00 10210.00 20.00 20.60 0.00 51.00

WAYNE JOHNSON #1 10456.00 6.00 19.70 6.90 56.20 10457.00 69.00 21.80 9.50 48.00 10458.00 29.00 21.20 9.80 51.70 10459.00 27.00 19.60 9.70 47.80 10460.00 0.01 5.50 6.20 88.90 10461.00 0.01 4.60 0.00 96.00 10462.00 0.01 5.40 0.00 80.00 10463.00 0.01 6.10 0.00 82.00 10464.00 0.01 5.20 0.00 85.70 10465.00 0.01 4.80 0.00 80.00 10466.00 0.01 5.90 0.00 88.90 10467.00 0.67 18.70 0.00 75.90 10468.00 0.73 18.50 0.00 74.50 10469.00 0.19 15.10 0.00 80.90 10470.00 0.06 14.80 . 0.00 79.30 10471.00 0.53 16.50 0.00 81.20 10472.00 0.76 16.60 0.00 76.70 10473.00 0.18 14.20 0.00 85.00 10474.00 0.13 15.80 0.00 79.80 10475.00 0.30 17.60 0.00 75.30 10476.00 0.43 15.80 0.00 73.40 10477.00 0.21 16.10 0.00 71.90 10478.00 0.36 15.90 0.00 76.20 10479.00 0.40 17.00 0.00 69.20 10480.00 0.33 16.90 0.00 71.40 10481.00 0.32 13.80 0.00 73.10 10482.00 0.45 13.50 0.00 71.10

AM0C0J.A.TH0MIII#2 10188.50 38.00 20.80 17.30 48.10 10189.50 0.83 8.70 0.00 63.60 10191.00 79.00 24.00 14.50 34.20 10192.00 121.00 23.90 14.60 43.10

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 310 10193.00 72.00 23.10 13.40 41.80 10194.00 97.00 22.40 12.50 41.70 10195.00 99.00 22.30 10.40 41.50 10196.00 99.00 23.40 12.70 44.90 10197.00 71.00 21.80 9.00 43.60 10198.00 50.00 22.20 13.50 41.40 10199.00 0.47 8.80 5.40 67.60 10200.00 28.00 23.60 12.30 42.60 10201.00 69.00 21.20 13.20 44.40 10202.00 82.00 23.70 13.60 43.50 10203.00 44.00 20.90 11.70 48.20 10204.00 19.00 19.80 12.40 46.30 10205.00 17.00 21.80 13.70 40.50 10206.00 16.00 21.20 11.80 43.70 10207.00 31.00 19.10 11.00 47.60 10208.00 69.00 22.00 13.20 47.00 10209.00 82.00 23.10 14.50 42.70 10210.00 13.00 18.20 12.60 43.70 10211.00 19.00 20.40 13.40 50.30 10212.00 17.00 20.40 12.70 45.50 10213.00 16.00 20.90 10.30 50.60 10214.00 15.00 19.20 10.30 49.20 10215.00 12.00 19.50 11.80 54.90 10216.00 10.00 19.00 9.10 57.40 10217.00 14.00 17.80 10.50 47.60 10218.00 18.00 20.10 12.20 50.70 10219.00 8.00 19.60 9.90 49.30 10220.00 14.00 20.10 10.60 52.80 10221.00 14.00 20.10 9.40 54.00 10222.00 34.00 23.30 9.60 54.80 10223.00 77.00 23.80 14.00 38.50 10224.00 10.00 18.90 3.60 59.80 10225.00 16.00 20.50 3.00 59.10 10226.00 11.00 19.90 1.80 63.20 10227.00 23.00 21.10 0.00 66.70 10228.00 138.00 22.10 0.00 66.70 10229.00 9.10 20.50 7.10 57.50 10230.00 14.00 21.60 0.00 64.20 10231.00 7.90 20.40 0.00 62.10 10232.00 10.00 21.20 0.00 70.60 10233.00 13.00 20.40 0.00 65.80 10234.00 6.10 20.90 0.00 66.40 AMOCO IPCO #1 10377.00 9.20 20.10 0.00 84.20 10377.50 6.40 19.10 0.00 78.60 10378.00 2.30 19.70 0.00 81.80 10378.50 4.40 19.10 0.00 72.60 10379.00 8.90 20.70 0.00 82.60 10379.50 28.00 22.80 7.60 75.60 10380.00 7.40 20.30 4.20 84.60

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 311 10380.50 6.50 19.40 2.00 83.80 10381.00 7.90 19.50 1.80 79.30 10381.50 3.60 18.60 1.70 80.30 10382.00 5.20 20.00 1.40 79.40 10382.50 2.20 17.80 1.70 86.80 10383.00 3.60 17.60 0.00 82.00 10383.50 8.60 20.10 1.20 78.00 10384.00 201.00 25.20 9.20 68.70 10384.50 30.00 21.10 7.30 73.30 10385.00 6.10 18.10 3.90 74.30 10385.50 210.00 23.40 8.10 70.80 10388.00 185.00 25.10 8.50 63.00 10386.50 200.00 24.80 9.40 68.10 10387.00 98.00 23.60 7.10 70.30 10387.50 170.00 24.00 8.00 68.20 10388.00 3.90 18.80 1.60 79.80 10388.50 25.00 22.60 10.10 64.00 10389.00 100.00 23.60 7.40 64.00 10389.50 160.00 24.70 9.60 66.30 10390.00 120.00 24.50 9.40 47.90 10390.50 66.00 23.10 12.20 56.70 10391.00 32.00 21.30 7.80 63.40 10391.50 20.00 22.00 9.00 63.80 10392.00 7.70 20.10 2.90 58.50 10392.50 33.00 24.30 7.60 71.10 10393.00 25.00 21.90 6.40 75.00 10393.50 8.20 19.60 1.50 78.50 10394.00 7.00 19.40 1.00 78.40 10394.50 40.00 23.50 0.00 77.60 10395.00 1.60 18.80 0.00 75.00 10395.50 2.40 19.10 0.00 77.40

BARNETT HE1RS#4 10160.00 31.00 19.30 12.30 44.40 10161.00 34.00 20.00 13.00 41.60 10162.00 42.00 20.10 11.60 43.30 10163.00 29.00 21.00 12.60 44.10 10164.00 46.00 22.40 10.80 43.30 10165.00 11.00 20.80 12.30 43.10 10166.00 30.00 23.20 10.70 39.70 10167.00 36.00 22.40 10.10 37.80 10168.00 31.00 23.10 12.00 40.00 10169.00 63.00 21.30 11.10 39.30 10170.00 83.00 22.30 10.50 41.10 10171.00 48.00 22.40 12.20 44.30 10172.00 61.00 21.80 10.10 42.90 10173.00 51.00 23.90 11.30 41.50 10174.00 57.00 24.50 11.20 41.00 10175.00 65.00 20.40 11.50 46.90 10176.00 0.02 6.80 6.80 58.20 10177.00

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 312 10178.00 18.00 19.00 8.60 39.70 10179.00 0.98 13.40 8.00 38.90 10180.00 0.01 7.30 9.30 56.00 10181.00 0.02 4.40 0.00 56.20 10182.00 0.02 3.90 0.00 61.50 10183.00 0.01 4.50 0.00 60.00 10184.00 6.20 16.20 7.00 46.00 10185.00 8.70 18.20 9.60 44.20

BARNETT #1 12324.00 205.00 20.20 0.00 60.00 12325.00 68.00 16.70 0.00 45.70 12326.00 34.00 18.50 1.00 69.30 12327.00 62.00 18.90 0.00 73.80 12328.00 3.50 16.00 0.00 63.30 12329.00 20.00 16.50 0.00 57.80 12330.00 30.00 19.00 0.70 64.30 12331.00 33.00 16.20 0.00 58.10 12332.00 1.30 10.60 0.00 52.90 12333.00 3.80 15.80 0.00 68.50 12334.00 37.00 18.70 0.00 75.60 12335.00 6.70 16.50 0.00 56.80 12336.00 23.00 18.80 0.00 60.50 12337.00 81.00 19.80 0.00 56.60 12338.00 9.60 16.90 1.80 62.50 12339.00 34.00 17.70 0.00 60.80 12340.00 37.00 17.50 0.00 42.90 12341.00 5.40 17.40 0.00 62.70 12342.00 13.00 18.10 0.00 71.50 12343.00 40.00 18.90 0.00 73.60 12344.00 2.90 16.40 1.00 77.40 12345.00 6.90 15.80 1.00 67.10 12346.00 3.20 14.60 0.00 53.30 12347.00 332.00 19.40 0.00 77.50 12348.00 3.70 16.70 0.00 65.50 12349.00 1.30 15.90 0.00 63.00 12350.00 6.00 16.30 1.30 55.90 12351.00 12.00 17.70 0.00 72.80 12352.00 8.70 19.70 0.00 75.00 12353.00 1.10 14.00 2.00 66.80 12354.00 4.00 18.90 0.90 73.80 12355.00 0.93 18.00 0.00 62.30 12356.00 7.00 18.30 0.00 68.20 12357.00 0.01 4.00 0.00 60.00 12358.00 0.01 3.80 0.00 66.70 12359.00 0.01 5.80 0.00 65.20 12360.00 0.01 5.90 0.00 70.60 12361.00 0.74 13.10 0.00 69.80 12362.00 0.20 14.50 0.00 66.70 12363.00 0.92 13.60 0.00 74.10 12364.00 0.42 13.30 0.00 69.50

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VANCE #1 10191.00 60.00 21.80 13.80 51.40 10192.00 58.00 18.50 10.60 59.20 10193.00 69.00 21.50 11.40 56.10 10194.00 60.00 22.70 11.00 51.40 10195.00 60.00 22.10 11.10 52.80 10196.00 55.00 23.00 9.90 55.90 10197.00 52.00 22.00 11.00 52.10 10198.00 29.00 20.50 6.50 57.90 10199.00 36.00 22.00 6.20 60.80 10200.00 34.00 21.60 0.00 67.20 10201.00 64.00 20.80 0.00 58.30 10202.00 35.00 19.30 0.00 71.70 10203.00 64.00 20.90 0.00 77.50 10204.00 34.00 20.20 0.00 64.00 10205.00 25.00 19.60 0.00 70.80 10206.00 27.00 20.50 0.00 76.00 10207.00 24.00 18.80 • 0.00 64.80 10208.00 17.00 18.20 0.00 61.50 10209.00 17.00 18.10 0.00 64.30 10210.00 13.00 18.40 0.00 61.90 10211.00 23.00 19.80 0.00 73.30 10212.00 26.00 19.60 0.00 71.40 10213.00 18.00 19.60 0.00 77.30 10214.00 12.00 18.40 0.00 73.50 10215.00 15.00 18.60 0.00 69.80 10216.00 16.00 18.80 0.00 67.60 10217.00 114.00 22.40 0.00 72.30 10218.00 156.00 23.80 0.00 72.90 10219.00 165.00 21.00 0.00 71.10 10220.00 4.65 17.10 0.00 69.90 10221.00 12.00 20.40 0.00 72.50 10222.00 21.00 20.40 0.00 68.60 10223.00 13.00 19.20 0.00 70.00 10224.00 16.00 21.10 0.00 69.60

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GALLON SIBLEY 10265.00 117.00 22.40 0.00 69.20 10266.00 66.00 21.30 0.00 70.60 10267.00 45.00 21.00 0.00 71.90 10268.00 146.00 22.20 0.00 70.00 10269.00 168.00 22.30 0.00 70.20 10270.00 126.00 22.40 0.00 71.10 10271.00 129.00 21.10 0.00 72.10 10272.00 53.00 21.00 0.00 70.70 10273.00 72.00 20.90 0.00 73.20 10274.00 70.00 20.80 0.00 72.50 10275.00 78.00 20.90 0.00 72.60 10276.00 75.00 21.00 0.00 72.90 10277.00 35.00 20.00 0.00 72.40 10278.00 66.00 21.10 0.00 73.00 10279.00 48.00 21.30 0.00 70.70 10280.00 55.00 21.20 0.00 71.60 10281.00 57.00 21.20 0.00 72.90 10282.00 63.00 21.60 0.00 73.30 10283.00 45.00 21.10 0.00 73.00 10284.00 43.00 21.30 0.00 72.60 10285.00 37.00 21.00 0.00 72.40 10286.00 41.00 20.00 0.00 73.40 10287.00 28.00 19.60 0.00 71.90 10288.00 30.00 19.90 0.00 72.60 10289.00 25.00 20.70 0.00 71.60 10290.00 27.00 20.90 0.00 72.70 10291.00 24.00 19.20 0.00 73.40 10292.00 22.00 18.30 . 0.00 73.60 10293.00 28.00 19.00 0.00 73.70 10294.00 27.00 19.10 0.00 70.00 10295.00 22.00 17.40 0.00 71.50 10296.00 101.00 21.50 0.00 72.30 10297.00 99.00 22.00 0.00 72.40 10298.00 24.00 18.60 0.00 70.90 10299.00 9.20 17.00 0.00 74.60 10300.00 16.00 16.70 0.00 75.70 10301.00 14.00 15.90 0.00 76.60 10302.00 24.00 19.20 0.00 73.80 10303.00 25.00 19.50 0.00 73.50 10304.00 10.90 16.80 0.00 79.20 10305.00 10.40 16.70 0.00 77.00

REID ERICKSON 10119.00 0.77 14.40 0.00 89.70 10120.00 0.01 14.30 0.00 75.00 10121.00 0.08 11.70 0.00 80.60

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GJ M O 321 10246.00 58.00 20.10 0.00 78.70 10247.00 80.00 21.20 0.00 80.60 10248.00 68.00 20.00 0.00 78.00 10249.00 79.00 21.30 0.00 84.40 10250.00 58.00 20.80 0.00 79.70 10251.00 47.00 20.20 0.00 81.10 10252.00 33.00 19.60 0.00 76.30 10253.00 36.00 20.90 0.00 75.20 10254.00 37.00 20.30 0.00 76.10 10255.00 45.00 19.90 0.00 68.30 10256.00 36.00 20.00 0.00 70.80 10257.00 57.00 21.10 0.00 74.30 10258.00 121.00 22.40 0.00 74.00 10259.00 124.00 22.30 0.00 72.00 10260.00 23.00 19.60 0.00 70.60 10261.00 31.00 20.50 0.00 72.00 10262.00 44.00 21.90 0.00 65.00 10263.00 23.00 20.30 0.00 70.90 10264.00 30.00 20.40 0.00 75.20 10265.00 24.00 19.70 0.00 62.40 10266.00 20.00 19.50 0.00 72.00 10267.00 14.00 19.20 0.00 56.30 10268.00 22.00 20.10 0.00 78.60 10269.00 19.00 20.00 0.00 70.60 10270.00 24.00 20.00 0.00 69.40 10271.00 12.00 19.80 0.09 67.70 10272.00 19.00 20.30 0.00 66.40 10273.00 16.00 20.00 0.00 67.00 10274.00 13.00 20.30 0.00 67.60 10275.00 9.14 19.40 0.00 64.80 10276.00 11.00 20.00 0.00 67.80 10277.00 11.00 19.90 0.00 66.20 10278.00 16.00 20.60 0.00 68.70 10279.00 3.31 16.20 0.00 61.60 10280.00 1.85 15.80 0.00 66.70 U.S. Howell #1 10286.00 42.00 20.20 1.30 74.20 10287.00 35.00 20.50 0.00 82.00 10287.00 32.00 19.80 0.00 78.40 10288.00 28.00 20.20 0.00 71.50 10289.00 20.00 21.90 0.00 69.30 10290.00 33.00 21.50 0.00 73.40 10291.00 29.00 21.60 0.00 63.80 10292.00 30.00 21.20 0.00 65.90 10293.00 29.00 21.00 0.00 63,20 10294.00 34.00 21.30 0.00 58.90 10295.00 25.00 21.40 0.00 59.20 10296.00 36.00 20.10 0.00 57.70 10297.00 35.00 20.90 0.00 59.10 10298.00 40.00 21.00 0.00 58.40 10299.00 30.00 20.70 0.00 62.30

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 322 10300.00 17.00 19.60 0.00 60.00 10301.00 29.00 21.20 0.00 58.70 10302.00 38.00 19.10 0.00 70.60 10303.00 21.00 21.70 0.00 64.30 10304.00 27.00 21.10 0.00 59.10 10305.00 24.00 22.70 0.00 59.60 10306.00 92.00 20.90 0.00 57.10 10307.00 27.00 20.30 0.00 62.50 10308.00 22.00 20.60 0.00 61.20 10309.00 11.00 20.10 0.00 60.70 10310.00 18.00 18.00 0.00 65.30 10311.00 10.00 20.20 0.00 53.60 10312.00 13.00 20.70 0.00 63.00 10313.00 16.00 19.30 0.00 61.50 10314.00 7.00 21.00 0.00 63.00 10315.00 19.00 20.50 0.00 53.40 10316.00 7.00 19.50 0.00 60.60 10317.00 11.00 21.00 0.00 61.50 10318.00 19.00 24.10 0.00 55.60 10319.00 7.40 18.80 0.00 66.90 10320.00 3.60 19.30 0.00 62.80 10321.00 3.00 17.60 0.00 62.50 Vida Smith #1 10350.00 8.30 26.60 0.00 84.00 10368.00 16.00 24.90 0.00 69.50 IstWXRASUQM.l. STEWART #1 10177.00 0.01 9.60 0.00 83.10 10178.00 125.00 23.80 15.00 45.00 10179.00 180.00 23.40 14.00 43.00 10180.00 120.00 22.70 12.90 43.10 10181.00 110.00 23.00 14.80 44.00 10182.00 28.00 21.20 13.70 45.80 10183.00 60.00 21.40 . 15.50 43.10 10184.00 55.00 19.80 14.60 41.70 10185.00 35.00 21.60 11.90 47.00 10186.00 41.00 21.80 11.90 47.40 10187.00 51.00 20.60 10.80 49.00 10188.00 44.00 20.80 11.50 50.80 10189.00 49.00 21.50 11.20 53.70 10190.00 42.00 21.10 12.30 45.30 10191.00 33.00 20.80 10.50 52.60 10192.00 34.00 21.40 8.90 56.80 10193.00 29.00 22.60 10.50 50.40 10194.00 32.00 20.70 13.50 41.70 10195.00 30.00 20.10 9.80 49.00 10196.00 26.00 20.30 11.60 50.00 10197.00 20.00 20.40 10.80 50.50 10198.00 6.90 18.60 12.10 48.40 10199.00 31.00 19.70 6.40 53.20 10200.00 25.00 20.20 8.30 59.10 10201.00 22.00 19.80 7.70 56.90

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 323 10202.00 13.00 19.00 5.40 59.80 10203.00 12.00 19.50 1.20 65.10 10204.00 81.00 21.40 6.50 55.20 10205.00 65.00 20.80 14.80 51.10 10206.00 0.15 12.10 2.70 59.30 10207.00 24.00 23.50 2.20 60.20 10208.00 0.03 8.10 2.30 72.70 10209.00 0.21 9.80 2.90 50.70 10210.00 4.55 15.20 2.90 64.30 10211.00 5.29 17.40 0.00 69.60 10212.00 4.52 17.00 1.10 59.80 10213.00 5.05 18.20 0.00 64.20 10214.00 7.27 18.80 0.00 69.90 10215.00 4.62 18.30 0.00 63.30 10216.00 5.98 19.00 0.00 71.90 10217.00 8.72 19.70 0.00 61.80 10218.00 6.83 19.30 0.00 69.40 10219.00 8.97 20.10 0.00 76.70 10220.00 2.89 17.50 0.00 65.30 CROWN ZELLERBACH N0.4 WELL 10201.00 0.01 5.60 0.00 81.50 10202.00 0.01 6.60 0.00 93.00 10203.00 36.00 18.30 8.90 56.20 10204.00 68.00 22.30 9.80 58.00 10205.00 67.00 22.80 12.10 53.00 10206.00 59.00 21.50 12.50 51.50 10207.00 47.00 22.30 13,10 49.20 10208.00 75.00 23.80 11.00 57.80 10209.00 40.00 22.20 13.80 48.80 10210.00 125.00 22.30 13.50 40.60 10211.00 60.00 21.30 11.10 53.20 10212.00 64.00 22.50 9.90 51.10 10213.00 73.00 23.00 11.20 49.10 10214.00 52.00 21.20 10.30 55.20 10215.00 60.00 21.80 11.80 47.10 10216.00 60.00 22.90 10.50 52.40 10217.00 42.00 20.80 8.30 58.30 10218.00 17.00 19.90 13.00 45.70 10219.00 49.00 21.10 11.30 49.30 10220.00 140.00 23.70 10.10 44.60 10221.00 195.00 24.10 16.00 43.20 10222.00 205.00 24.70 13.50 42.60 10223.00 170.00 23.80 17.50 47.50 10224.00 24.00 18.70 1.70 55.80 10225.00 27.00 20.90 1.40 61.20 10226.00 26.00 19.90 0.00 64.40 10227.00 25.00 21.70 1.80 61.60 10228.00 11.00 20.40 0.00 68.00 10229.00 21.00 21.20 2.00 60.40 10230.00 36.00 22.40 0.00 62.10 10231.00 24.00 22.30 0.00 61.30

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 324 10232.00 23.00 22.10 0.00 61.00 10233.00 16.00 20.70 0.00 60.90 10234.00 22.00 21.30 0.00 70.70 10235.00 29.00 22.20 0.00 74.80 10236.00 11.00 21.90 0.00 58.80 10237.00 18.00 21.80 0.00 58.80 10238.00 8.35 20.90 0.00 59.30 10239.00 8.49 21.10 0.00 66.30 10240.00 6.07 19.40 0.00 55.90 10241.00 1.92 17.80 0.00 61.00 10242.00 0.20 13.90 0.00 69.60 RAY MORRISON N0.1 WELL 10243.00 24.00 20.70 0.00 65.50 10245.00 97.00 23.50 0.00 63.60 10246.00 54.00 21.70 O.OG 59.20 10247.00 76.00 22.50 0.00 62.50 10248.00 72.00 24.10 0.00 61.90 10249.00 58.00 21.80 0.00 63.30 10250.00 44.00 22.70 0.00 65.40 10251.00 47.00 20.40 0.00 60.30 10252.00 43.00 20.40 0.00 69.20 10253.00 41.00 22.00 0.00 65.80 W. DOYLE JONES ET AAL N0.1 10295.00 0.04 10.50 0.00 73.70 10296.00 15.00 21.60 0.00 86.70 10297.00 36.00 22.30 0.00 91.00 10298.00 156.00 24.60 0.00 81.10 10299.00 76.00 23.90 0.00 80.00 10300.00 111.00 22.10 0.00 88.90 10301.00 51.00 21.10 0.00 89.30 10302.00 12.00 20.50 0.00 91.30 10303.00 23.00 21.40 0.00 84.20 10304.00 31.00 19.80 0.00 81.10 10305.00 29.00 19.30 0.00 92.00 10306.00 26.00 21.10 0.00 91.10 10307.00 40.00 20.80 0.00 86.10 10308.00 66.00 22.00 0.00 90.80 10309.00 72.00 20.80 0.00 86.20 10310.00 14.00 19.70 0.00 92.00 10311.00 13.00 20.70 0.00 85.60 10312.00 18.00 20.20 0.00 88.00 10313.00 17.00 21.10 0.00 85.50 10314.00 24.00 20.80 0.00 89.20 10315.00 36.00 22.50 0.00 79.80 10316.00 20.00 22.90 0.00 81.00 10317.00 21.00 21.30 0.00 89.50 10318.00 29.00 21.80 0.00 93.70 10319.00 15.00 18.70 0.00 83.60 10320.00 9.90 19.80 0.00 73.70 10321.00 10.00 19.30 0.00 74.50 10322.00 7.30 20.70 0.00 75.80

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 325 10323.00 5.30 20.00 0.00 78.50 10324.00 40.00 19.30 0.00 82.50 10325.00 80.00 21.80 0.00 97.20 10326.00 4.50 18.30 0.00 78.60 10327.00 5.60 21.10 0.00 85.40 10328.00 5.10 23.00 0.00 82.60 10329.00 3.20 19.50 0.00 80.40 10330.00 4.30 20.00 0.00 74.40 10331.00 94.00 20.90 0.00 84.40 10332.00 85.00 22.80 0.00 80.70 10333.00 3.20 19.80 0.00 81.20 B.C. HOWELL N0.1 WELL 10364.00 80.00 25.70 8.00 61.10 10368.00 74.00 24.30 15.40 58.90 10370.00 41.00 23.30 17.50 62.10 10372.00 36.00 22.90 16.20 55.50 10374.00 55.00 23.70 12.70 55.30 10376.00 22.00 24.20 9.20 63.30 10377.00 5.40 20.70 3.70 74.40 10378.00 50.00 23.50 3.20 80.80 10385.00 20.00 23.90 0.00 81.10 10386.00 22.00 22.10 0.00 74.70 10387.00 15.00 21.80 0.00 77.30 10388.00 21.00 21.20 0.00 75.20 10389.00 33.00 22.60 0.00 78.60 10390.00 13.00 20.20 0.00 80.00 10391.00 44.00 23.80 0.00 80.00 J.A. THOM N0.3 10203.00 62.00 20.30 18.20 40.20 10204.00 106.00 23.20 16.90 39.50 10205.00 37.00 21.70 14.90 44.00 10206.00 25.00 22.70 11.50 44.80 10207.00 23.00 20.90 11.50 48.20 10208.00 24.00 20.80 11.50 51.30 10209.00 34.00 22.40 12.40 50.30 10210.00 23.00 20.60 12.70 48.10 10211.00 25.00 21.00 12.10 51.00 10212.00 33.00 20.60 12.30 50.00 10213.00 16.00 19.00 7.60 52.20 10214.00 21.00 20.40 7.40 51.50 10215.00 46.00 21.00 13.10 50.60 10216.00 34.00 20.70 11.50 52.50 10217.00 33.00 19.60 9.00 55.20 1.0218.00 29.00 19.40 11.80 57.60 10219.00 36.00 19.50 5.90 53.80 10220.00 36.00 21.00 9.60 53.70 10221.00 30.00 22.00 9.60 51.90 10222.00 43.00 21.70 11.20 48.40 10223.00 100.00 21.00 13.70 48.70 10224.00 26.00 19.30 9.30 55.80 10225.00 19.00 17.90 9.90 54.20

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX C

LISTING OF WELLS USED TO CONSTRUCT REGIONAL STRUCTURE MAP AND CROSS-SECTIONS

326

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 327 COMPANY WELL LOCATION TOP WILCOX

GEO. M. HARRISON USA #1 T3N-2E-2 -4608 HUGHES &NEW OIL CO. #1 OFALLON PLANTATION UNIT T3N-4W-42 -5570 FIRST ENE K. MUNSON #1 T3S-1E-37 -8610 PENNINGTO K. MUNSON #2 T3S-1E-58 -8620 EXCHANGE W.T. PRICE #1 T3S-1E-63 -8060 EXCHANGE E.J.LANONEETAL# T3S-1W-12 -8050 CLOVELLY J.T. HOWELLETAL# T3S-1W-40 -7857 FIRST ENE SL 9254 #1 T3S-1W-42 -7935 COTTON A.C. MCKEOWN JR #1 T3S.1W-50 -8350 JEM PETR. J.T. HOWELL #1 T3S-1W-84 -8250 COTTON ROBERT MCGILL #1 T3S-1W-86 -8290 CLOVELLY J.T. HOWELL #1 T3S-1W-93 -8128 CONTINENT DEVILLE #7 T3S-2E-46 -9479 PHILLIPS JONES "AA" #1 T3S-2E-76 -7948 MONCRIEF ROSEDOWN PLANT. #1 T3S-2W-10 -8440 S. LA PRO P.C. WITTER #1 T3S-2W-96 -8460 SHELL OIL FISHER #1 T3S-4E-10 -9285 WESTLAND H0RECKY#1 T3S-4E-16 -9380 MARTIN EX DELAHOUSAYE#! T3S-4E-17 -9455 TEXAS PAC TAYLOR #1 T3S-4E-22 -9545 TEXAS PAC NATALBANYLBRCO.# T3S-4E-26 -7260 HUGHES & M. DID0MENCIA#1 T3S-4E-48 ■ -7400 GETTY HARVELL #1 T3S-4E-50 -7444 HUNTENEGRYCORP GEORGIA PACIFIC #1 T3S-4W-22 -91 1 5 WAMONC THISTLETHWAITEETA T3S-5E-10 -9350 CHEVRON TURNER LUMBER #1 T3S-5E-14 -8303 SHELL ROBERTSON #1 T3S-6E-16 -6572 SHELL OIL MYERS #1 T3S-6E-17 -9445 CROSBY DR GORDON #1 T3S-6E-2 -9154 SHELL OIL TURNER LUMBER#1 T3S-6E-20 -9480 SHELL OIL TURNER #3 T3S-6E-21 -9500 BISOURCE DENKMAN ASSOC #1 T3S-6E-22 -6579 SHELL OIL MARTIN LUMBER #1 T3S-6E-25 -9636 SHELL OIL WOODLAWN #1 T3S-6E-3 -9095 SHELL OIL MARTIN LUMBER #2 T3S-6E-36 -9745 GULF OIL TURNER LUMBER #2 T3S-6E-5 -8974 ASHLAND R.D. BRIDGES #1 T3S-6E-55 -6368 ASHLAND E J.H. MORGAN #1 T3S-6E-55 -6454 LAMAR RIC #1 BILLUPS T3S-6E-56 -6566 MCUNTON J.W. COLE #1 T3S-6E-6 -6476 CHEVRON LOWREYHEIR#3 T3S-7E-10 -9594 SHELL OIL JARREL #1 T3S-7E-13 -9655 SHELL OIL R.L. WOLFE #2 T3S-7E-13 -9741 PENZOIL LAB0RDE#1 T3S-7E-22 -9065 LOUTEXEN WATSON #1 T3S-7E-31 -9535 SAMEDANO J. SEARCY #1 T3S-7E-4Û -6238 CHEVRON DELANO PLANTATION# T3S-7E-7 -9481 MONCRIEF LEE #1 T3S-8E-38 -8745 O&G FUTUR M.E. DAVIDSON EST#1 T3S-8E-38 -5850 LAMAR HUN LACOUR #1 T3S-8E-42 -8845 SOUTHERN LAC0UR#3 T3S-9E-37 -8486 DORRIS BALLEW INC BOARD OF SUPERVISORS #1 T4N-2E-18 -4366 DAMSON A.LANGL0IS#1 T4S-10E-2 -9100 AMOCO G. BEAUD#1 T4S-10E-3 -9825 SINCLAIR BEAUD #1 T4S-10E-3 -9606 AMAREX MAJOR #1 T4S-10E-4 -9782 OCNCOO SCHEXNAYDER#2 T4S-10E-5 -9640 AMOCO A.J. MIX #1 T4S-10E-52 -1 0000 AMOCO J.T. BUTLER #1 T4S-10E-54 -10000

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REGIONAL WELL LOG CROSS-SECTIONS (Located In cover pocket)

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Philip Lowry was born in Belfast, Northern Ireland on August 27, 1956, the second child of Henry and Ellen Lowry. He completed his Primary education at the Braniel Primary School and Secondary education at Lisnasharragh Secondary School in Belfast. His 'A' level studies were completed at Cregagh Technical College also in Belfast.

From 1975 to 1978 he studied for the degree of Bachelor of Science in Environmental Science at the University of Ulster at Coleraine, Northern Ireland and obtained a second class upper division honours degree in 1978. He began work on a Master of Philosophy degree at the University of Ulster in 1978. The subject of his thesis was morphodynamics of modern coastal depositional systems. He received his Master of Philosophy degree in 1982. In 1980, he entered Florida State University to pursue a doctoral degree in Geology focusing on modern coastal stratigraphy. In 1982 he transferred to Louisiana State University in Baton Rouge to become involved in the study of both modern and ancient depositonal systems. While at LSU he was involved in teaching undergraduate Historical geology as well as participating in a variety of projects on modern depositional systems.

He has published papers on numerical modeling of modern coastal process-response systems. He has also presented several papers at national and regional geological conferences The subjects of these papers range from recent stratigraphy of the Alaskan Beaufort Sea to stratigraphie sequences in the Tertiary of the Gulf Coast. Upon completion of his doctorate he began work with Shell Offshore Inc. as a geologist. He and his wife Dianne currently live in New Orleans, Louisiana and have one daughter, Caitlin Julia.

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Candidate: P h ilip Lowry

Major Field: G eology

Title of Dissertation: "S tratig rap h ie Framework and Sedim entary Facies o f a C lastic Shelf-M argin: Wilcox Group (Paleocene-Eocene) Central Louisiana."

Approved:

Major Profe^df^^d Chairman

Dean of the Gradudce School

EXAMINING COMMITTEE:

. Æ j û i è l - — ■

Date ot Examination:

A p r i l 2 2 , 1987

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Jamajo industries Pan American Pet. Corp. J. E. Thornhill Hunt Oil Co. Walker Nolan #A-1 Joffrion # 3 Holmes #1 B. F. Lemoine #1 S26-T1N-R3E S18-T1N-R6E S34-T1N-R6E S26-T1N-R6E

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E Hughes & New Oil Placid Radzewicz Bamwell Drilling Hunt Ener # 1 OTallon # 1 Sessions 24-9 #1 Joe Fausi Barnwell Feliciana #1 Georgia Pi 42 3N-4W 24-2N-4W 40-1N-4W 46-2S4W 22-3S4W j

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